The princess hall is a small location in Moria, made for the elf princess. She was won by the king dwarf during the great war.
It is placed in a small ravine, far from the other dwarfs. The only one who was allowed entrance was servants and the king. The sad princess missed the outdoor woods and swamps of the elfs, so the king made the floor of sandstone and wood. He also installed some glass windows, with torches inside, to remind her of the outside view from above ground. Looking “out of the window” seeing just rock and a torch, the princess killed herself.