The Surface Level
This is the actual "necromancer's garden". It was a small fortress on a hilltop with a set of four crypts built within the fortress walls. The crypts have been vandalized and in the case of two of the crypts, smashed wide open by some potent force years ago.
Two of the crypts have secret stairwells that lead to the underlevels. One is exposed from the damage (although the secret door remains secret - the walls around the stairwell are missing). There is also a stairwell to the dungeons under the fortress.
This was the original map of the set that went on to inspire the side view and sublevel maps.