There was no 'landmark' concentration camp. If you mean 'best known' or 'notorious' then the answer is Auschwitz, most of which was developed between 1940 and 1942, using in part existing building dating from 1900-1910.
No, Stutthof was the first concentration camp built outside Germany. (The first camp was Dachau).
A concentration camp.
Buchenwald, though initially it was called Ettersberg (for a couple of weeks or so).
the first permanent Nazi concentration camp was built near Munich.
Hitler designed Dachau concentration camp but it was the people who was going to be in it who built it.
the Nazis
the concentration camp was built in 1940.
No, it was the main camp that the Nazis built in Austria.
Mainly in 1942, it was an extension to the existing concentration camp.
The Buna camp (Monowitz, Auschwitz III) made various plastics for I.-G. Farben. It was the first concentration camp built by private entreprise.
The Bergen-Belson
generally they had purpose built barracks.