The entry building to the Birkenau camp (BW9), which has become infamous as the "Gate of Death," was built in two stages. The main entryways (rail and road) were built in 1942 and the side wing that appears to the right of the tower was added in 1943, for a transformer station. The object on top of the tower roof, that sometimes appears to be a cross in photos, was a siren. The single rail line entering the camp came from the area of the Judenrampe, and was added in the spring of 1944 to permit detraining of deportees directly in the camp, close to Crematoria 2 and 3.  (Google Maps link)

The images below show the view from inside the camp, looking out. The single rail line that entered the camp split into three tracks inside. The period view, taken shortly after the liberation in January 1945, shows a pile of pots, pans, and other deportee belongings lying on the rails, as well as camouflage stripes painted on the gate building.  (postwar postcard)

Original rail switching apparatus and rails still exist in Birkenau. The unloading ramp for arriving prisoners is the partly buried concrete structure seen to the right of the rails in the photo on the right. The flimsy wooden towers seen along the fence lines on either side of the rail area are all postwar replicas of the guard towers that once stood there. (See here for the ramp "selection process.")

The Birkenau camp was divided into three sections, or Lagers. Lager BI, on the south side of the rail lines, had some brick barracks (BW3a) and some wooden barracks (BW3b); only the brick barracks (and one wooden barrack) survive. The locations of the wooden barracks are marked today by the ruins of their brick stoves and chimneys (above left - note that many of the standing chimneys were rebuilt after the war from scattered bricks by the Museum personnel (Ref. 2, page 133). Lager BI was first built for (and by) Soviet prisoners of war, but it soon became a camp for male deportees. In July 1943 Lager BI was converted to a women's camp, which it remained until all prisoners were relocated in November 1944 to Lager BII (after which Lager BI remained empty). The women's barrack above shows some of the conservation efforts to shore up the walls of these brick buildings until they can be repaired and preserved. The women slept on wooden bunks in the cold uninsulated barracks which were barely heated by small stoves. The period label SEI RUHIG! on the wall above the stove called for calm and quiet among the prisoners.  (Auschwitz-Birkenau State Museum, www.auschwitz.org) 

Block 13 in Lager BIa (renumbered to Block 16 in 1944) housed children for much of its existence. In 1942 these were Polish children with their mothers; in 1944 this barracks housed Jewish children from the Warsaw Ghetto. Inmates decorated some of the walls with scenes of children playing and going to school. In contrast to the dirt/mud floors of the other barracks, this Block had a floor paved with brick.

Block 25 of Lager BIa (above left) was called the "Death Barrack" because female prisoners who had been deemed unfit for work were kept there until they were sent to the gas chambers. In Block 28 (right above) newborn babies and their mothers were executed by phenol injections to the heart. In contrast to the horse stable type barracks in Lager BII, this barrack was of the so-called "Swiss" type, with windows, floors, and ceilings (a few of this type were also in Lager BIIf and BIIg). Below left is the site of Block 30, where sterilization experiments were performed on prisoners by SS doctor Carl Clauberg and others (see also here). Below right is the site of Block 31, which housed Jewish children in 1944, including twins and others used as subjects for medical experiments by SS doctor Josef Mengele.

The buildings in the left background of the photo of the Block 31 site above were latrine and washroom buildings, five in each of the two sections of Lager BI (BW7a). The latrines were very primitive facilities, with just holes in a long concrete bench.  (Yad Vashem Collections)

Two brick buildings in Lager BI, one in B1a (left above) and one in BIb (right above), were used for prisoner showers and delousing of clothing and bedding (BW5a). Before the "Sauna" was opened, initial registration for newcomers took place here. Most of the delousing was done by steam apparatus (see below), but the east wing (side wing) of the building in Lager BIb (below) was converted to use cyanide delousing chambers. The use of Zyklon B cyanide insecticide as a delousing agent in this wing produced the dark "prussian blue" staining visible in the bricks to this day. The scoop-shaped openings on the end wall of the east wing were for ventilation.

The "prussian blue" cyanide staining from the use of Zyklon B is visible on both sides of the delousing wing of building BW5a in Lager BIb, which had no windows (in contrast to the similar building in Lager BIa). The circular openings in the end wall of the wing allowed ventilation fans to circulate air following a Zyklon B delousing session.

The building is in poor shape on the inside today. The room at the left may have housed steam delousing apparatus. The wall on the right still bears the original logo "Eine Laus dein Tod" - "One louse, your death" - referring to the dangers of lice-born typhus epidemics in the camp.

A large kitchen building was provided in each of the two sections of Lager BI (left above). The building on the right above was a storehouse (BW4a) for clothing in Lager BIb (in the left background are the ruins of Crematorium II).

  Lager BII consisted of 180 wooden barracks and kitchen buildings, along with 18 wooden buildings for hospital wards, and six wooden Blockführer buildings – over 200 buildings in all (BW5d). The wooden barracks, which had been built on plans for horse stables, were each designed for 400 prisoners, but most housed hundreds more in very crowded conditions. The wooden barracks were almost all removed after the war, and all that remains of most of Lager BII today are the brick stoves and chimneys, and a couple of brick walls, surrounded by the ubiquitous concrete posts for the electrified barbed wire fencing. The view on the right above looks over Lagers BIIc and BIIb, toward BIIa. The remains below are in Lager BIId, part of the men's camp.  (Yad Vashem Collections)

The first row of barracks - Lager BIIa - served as a quarantine barracks for newly arrived male prisoners (converted to a warehouse area during the final two months of the camp's existence). Along with the living barracks were latrine barracks, consisting of very primitive facilities (below).  (Yad Vashem Collections)

Note - Guide books, reports, and tour guides from the Auschwitz-Birkenau Museum say that these wooden barracks buildings are the originals, but other sources (sometimes quoting Museum personnel) report that all the original wooden Birkenau barracks, except one, were torn down after the war, and the wood used during postwar reconstruction in Warsaw, and that the barracks we see today are rebuilt replicas (except one original, located behind these in Lager BIIb). See Ref. 1, page 10; Ref. 2, pages 33, 132-33; Ref. 6, pages 20, 22, 136.  (Auschwitz-Birkenau State Museum, www.auschwitz.org)

On the left is Block 30 of Lager BIIb, which is said to be the only original wooden barrack left in Lager BII. This is only half of the original barrack, the other half of which was on loan to the U.S. Holocaust Memorial Museum in Washington, DC, from 1989-2013. Although the walls and roofs are reportedly rebuilt, the beams of some of the Lager BIIa buildings appear to be original. The cross beam on the right above appears to bear original lettering HALTE ORDNUNG - Keep Order. (Note - The other half of Block 30 was re-erected here in late 2015 or early 2016.)

  This view of Lager BIIa was taken from the tower of the Birkenau gate building, looking north. This 1945 view was published as a postcard shortly after the war.

  At the north end of each section of Lager BII was an ornamental garden surrounding a stone well. These photos show the garden at the end of Lager BIId. The structure in the distance was a large elevated water tank for the kitchen barracks. Prisoners were sometimes executed in public near this water tank.  (Yad Vashem Collections)

On the left is one of several fire fighting reservoirs on the grounds of the Birkenau camps. These reservoirs were necessary because there were no water hydrants. The photo on the right shows the area of the so-called "football (soccer) pitch" (left of the fence line), a controversial feature that existed at the south end of Lager BIIf, near Crematorium III. Hungarian doctor Miklos Nyiszli, who worked in Birkenau with the SS doctors, reported that the SS guards played soccer once with the Sonderkommando on the grounds of Crematorium II, and Auschwitz-Birkenau Museum publications state that this area in Lager BIIf was also used as a soccer field. Note the deteriorated condition of some of the concrete fence posts, which have not yet been repaired.

On the left are the foundation ruins of barracks of Lager BIIf, the men's infirmary. These barracks were also used by the infamous SS doctor Josef Mengele in his medical experiments on children (mostly twins), dwarfs, and other individuals. The Lager BIII section, called "Mexico" by the prisoners, was on the other side of these deteriorating fence posts on the right.

This depot, built in late 1943, was where the confiscated personal property of prisoner arrivals in 1944 was sorted. At times, particularly during the large shipments of Hungarian Jews in May-June 1944, these 30 barracks were insufficient to hold all the loot, and piles of clothing and other goods appeared between the barracks, waiting sorting and storage. The photos above show the entry gate into "Canada II" on the south side. None of the buildings of "Canada II" exist today, as the depot was set on fire before the SS abandoned Birkenau in January 1945, although there is a small outdoor display of confiscated goods at the site of one of the buildings.  (Yad Vashem Collections)

This building, located at the far end of the "Canada" section, is called the "Sauna" (BW32). However, its official name was Entwesungsanlage - a delousing/disinfection facility, and it was no sort of traditional sauna. This building served the same purpose in Birkenau as the reception building in the Auschwitz main camp - those prisoners who were selected as laborers to be admitted to the concentration camp passed through this facility to be disinfected in showers, their hair was cut, their clothing was deloused and they were issued camp uniforms and registered in the system, all in this building. The building presents largely its original appearance, but some of this is due to reconstruction work after 1945.  (Yad Vashem Collections)

Arriving prisoners were processed through this large hall for registration.  (Yad Vashem Collections)

The prisoners passed through a hair cutting room (Haarschneideraum), shower (Brausen), examination room (Untersuchungsraum), and then picked up disinfected clothing (Desinfizierte Wäsche), all rooms still labeled today above their doorways.

Prisoners worked in the "sauna" building, delousing the clothing with steam and hot air apparatus. The period photos below shows racks of deloused clothing from one of the room type hot air delousing chambers. (Zyklon B was not used as a delousing agent in this building.)  (Yad Vashem Collections)

Several sewage treatment plants were built around the periphery of the Birkenau camp (BW18). These brick facilities remain in ruins today.  (Yad Vashem Collections)

Down the road from the "Gate of Death" entry building, opposite sections BII and BIII, was the Birkenau camp Kommandantur (headquarters - BW10). The SS Kaserne was directly behind this headquarters building, which is now a church (not part of the Auschwitz-Birkenau Museum). The SS barracks complex in the rear was torn down after the war.  (Yad Vashem Collections)  (Google Maps link)

Above - Adjacent to the Kommandantur was a waterworks building (BW35) for the SS Kaserne complex (including the Kommandantur and SS hospital complex). This building exists as a ruin today. Below - At the southeast corner of the camp, outside the perimeter, were two Kartoffellagerhalle potato storage warehouses, similar to those near the Judenrampe. One of these buildings exists today as a ruin.  (Yad Vashem Collections)