The base is four, concentric, fieldstone rings from the Fieldstone Castlemolds. They range from 7" on the outside to 4" on the inside. This was a bit of a casting nightmare. To get enough pieces I had to cast the molds 24 times, which took about two days of solid casting.
The central hole of the gazebo is ringed with "teeth" from another Castlemold. The premise is that this is a sacrificial altar. The evil wizard can bring his victims here and feed them to the gazebo. If I wanted to place the gazebo in an unoccupied area, perhaps it would have tentacles up inside the roof to grab curious adventurers and drop them into the gaping maw below.