Found two lairs in the T-1 RvR areas so far:
1. In Norsca, when at the RvR objective, there's a back exit, take that, swim to the closest island (take a left), then there's a closed cave there. To open it, stand on the rune that signify your race (and have others stand on their rune) - it should open up.
2. Lair of the Bandit Queen: Northwest in dwarf area, near the RvR objective where you have to grab bitterstone ore. When facing the mine, take a right and go up the hill, you'll end up at the lair. Apparently you have to kill an enemy player near the lair for it to open up (I didn't have the opportunity to test this)
I suppose the elf RvR area will have its own lair. I haven't so far found any lairs in T2. Unfortunately you get chickened when checking out the lower-tier lairs.
