That's why there were huge rocks left like that. Mauthausen had a famous death stair with 100 steps where prisoners often fell with heavy rocks on their backs. It had a very high death rate among the KLs in Nazi Germany, even though it wasn't an extermination camp like Auschwitz. The letter L in KL, i.e. larger in German means collection, storage, thus extended to the meaning of camp. Interestingly beer is also called larger. Maybe because beers need to be stored together. K is concentration in German.
House #15 is not marked because the government doesn't want it to become the worshiping or gathering place for the NeoNazis. Many things related with Hitler were either destroyed or unmarked for this reason.
