HoMM3 HD is a mod (add-on) for the game Heroes of Might and Magic 3.

Played on version 3.20 - Found a couple of empty dungeons. Not sure if it's fixed in 3.24. Played on HD+.

Empty dungeons occur because one of the starting heroes was supposed to be imprisoned there. This is a bug in the SoD (Shadow of Death) expansion. It's easy to check by looking at the dungeon in the map editor. But usually, there's only one such dungeon on the map, and if there are many, then it's probably something else.