The Villa Grimaldi was a private estate seized by Pinochet who used it as a prison, torture chamber, and place of execution for rival political opponents. (See, for example, http://en.wikipedia.org/wiki/Villa_Grimaldi)
The main house was destroyed by the army, so the grounds are primarily a park in honor of the victims.
There is a wall of the names if the victims, and names distributed throughout the rose garden.
The guard house, also destroyed by the army, but reconstructed, now contains glass cases with personal effects – a tie, glasses, schoolbook, etc. – of Pinochet’s victims.