OpenZone is a great tool, but hit its maximum when you want have a zone with a complex geometry. You might be able to create a black burrow zone like by playing with OpenZone and Dungeon Builder but it start to be a good challenge.
Another idea would be to use Q3 Radiant, but one of the big problem with radiant is you will have to force yourself to not do a Q3 like map
If you want to do complex zone, eqlive quality, the best thing is "hand edit", aka 3D Software, like 3DSMax / Maya, you can get GMax for free, its a great software. Those software will allow you to do impossible things with an editor.
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