There are a few generated structures in Nether X. As of version 1.3 there are nether dungeons that are pretty much like normal dungeons except that they are made with nether materials. Another structure is the stalactites and stalagmites that make up the spiked cavern biome. The third structures are the poison lakes found around the nether. The last structures are the vilewood trees. They are the only trees in the nether. There are also a few secret structures added that you should find and check out!