I took the tour here in English, but it is possible to do it in French (or any one of around 15 other languages).
Though partly destroyed, the site is still impressive. When you see the railway tracks and the wooden huts (former stables to which latrines were added), you can really imagine what the "living" conditions must have been like for the prisoners, and the very idea sends a shiver down your spine.
On the day I visited, the sun was shining brightly but the atmosphere was chilling. Seeing the remains of the crematoria and hearing what the tour guide has to say provides a vivid reminder of the horrors that took place here. Auschwitz-Birkenau is the largest Jewish cemetery in the world.
This is an absolutely essential place to see when visiting Poland, but when you come back out of this emotionally-charged site afterwards, you won't be quite the same as when you went in.