Whatever you've read or heard about the Nazi death camps, nothing is likely to prepare you for the shock of seeing them in person. Auschwitz is the best known of the two, though it's at Birkenau, south of Auschwitz, where you really see and feel the sheer scale of the atrocities. The precise number of deaths at the camps is unclear, but well over a million people were systematically killed in the gas chambers, or were hanged or shot or died of disease or exhaustion. Most of the victims were Jews, brought here from 1941 to 1944 from all around Europe, stuffed into rail cattle cars. In addition to Jews, thousands of POWs, including many Poles, Russians, and Gypsies (Roma), were exterminated here, too.
Most visitors start their exploration of the camps at Auschwitz, the first of three main concentration/extermination camps built in the area. (The third, Monowitz, was situated in a suburb of Oswiecim; it was abandoned after the war, and now all that's left is an open field. This is the camp where acclaimed writer Primo Levi, author of Survival in Auschwitz [Orion Press], was held.)
Auschwitz got its start in 1940, when the Germans requisitioned a former Polish garrison town, Oswiecim, for the purpose of establishing a prisoner-of-war camp. The first groups of detainees included Polish political prisoners and Russian POWs. Conditions were appalling, and in the first year alone, nearly all of the several thousand Russian POWs died of exhaustion and malnutrition. It was only later -- in 1942, after the Germans decided on a policy of exterminating Europe's Jewish population -- that Auschwitz became primarily a death camp for Europe's Jewry.
Admission to the Auschwitz museum is free, and you're allowed to roam the camp grounds at will, taking in the atrocities at your own pace. (If you're not employing a guide, be sure to pick up a copy of the Auschwitz-Birkenau Guidebook for 4 z, available at the small kiosk at the museum entrance. This booklet contains short explanations of the main sites and maps of the camps.) On entering the museum, you'll first have the chance to see a horrific 15-minute film of the liberation of the camp by the Soviet soldiers in early 1945. The film is offered in several languages, with English showings once every 90 minutes or so (if you miss a showing, you can always come back to see it later). After that, you walk through the camp gates -- passing below Auschwitz's infamous motto Arbeit Macht Frei (loosely translated as: Through Work, Freedom). Once inside, the buildings and barracks are given over to various exhibitions and displays.
Don't miss the exhibition at Block No. 4, "On Extermination." It's here where you'll see photos and descriptions of the system of rail transports, the brutal "selection" process to determine which of the new arrivals would go straight to the gas chambers and which would get a temporary reprieve to work, as well as the mechanics of the gas chambers. You'll also see actual canisters of the Zyklon-B gas used, and, in one particularly gruesome window display, yards and yards of human hair used to make rugs and textiles. Block No. 11 is called the "Death Block"; it's where prisoners were flogged and executed. Other blocks house national exhibitions, with particularly moving presentations from Poland, Hungary, and the Czech and Slovak republics (Block 16).
Birkenau, also known as Auschwitz II, lies about 2.5km (1 1/2 miles) to the south. It's larger, more open, and even (if possible) more ghastly than Auschwitz. It's here where most of the mass gas-chamber exterminations took place at one of the four gas chambers located at the back of the camp. To get to Birkenau, take a free shuttle bus situated not far from the main entrance. You can also walk (about 20 minutes) or take a taxi (around 10 z-15 z, but agree on a price in advance).
Birkenau appears almost untouched from how it looked in 1945. Your first sight of the camp will be of the main gate, the "Gate of Death." The trains ran through this entryway. The passengers were unloaded onto the platforms, where they were examined by Nazi SS doctors and their belongings confiscated. About 30% were chosen to work in the camp and the rest -- mainly women and children -- were sent directly to the gas chambers, just a short walk away. The scale is overwhelming -- prisoner blocks laid out as far as the eye can see. There are no films here and few resources for visitors (including no public restrooms). Instead, set aside an hour or so to walk around the camp to take it in. Don't miss the remains of the gas chambers situated toward the back of the camp, just to the right of the memorial to the Holocaust victims. The Germans themselves attempted to destroy the gas chambers at the end of 1944 and early 1945 to cover up their crimes once it was apparent the war could not be won. Now, little remains of them (but enough to get the general, gruesome idea). You can return to the main Auschwitz museum by foot, shuttle bus, or taxi, and from Auschwitz back to Kraków by bus or train.