you don't "pass" relic castle you go to it later and meet team plasma (you also get a fossil if you talk to the backpacker!)
In relic castle
it is the evolvtion of yamask so... it is rare in the relic castle
you have to get to the bottom
you must once more beat the elite 4 then the spot will gloe you go there!
Relic castle catacombs( the place in desert resort)at level 70 at the door the sage was blocking. You have to find your way through the maze.
It is a maze just like the last answer said. You must get the National Dex first, though.
U can walk in the quick sand you won't sink. Other than tha it is just a big confusing maze
Relic Castle
All you have to do is go to relic castle and WALK across the sand pits at the outer edge go to the back wall and go down the stairs. Then defeat team plasma!!!
if you cant get through it because you think its too difficult and stuff, search on youtube "how to get through relic castle in Pokemon black/white". There is no way you won't find a video that helps you in that. I got through victory road thanks to a walkthrough video on youtube, for example. Hope I helped :)
Relic Castle
Desert Resort.
you don't "pass" relic castle you go to it later and meet team plasma (you also get a fossil if you talk to the backpacker!)
By trade.
there is a backpacker in relic castle who will give you either a plume fossil (which is revived into an archen) or a cover fossil (which is revived into a tirtouga)
relic castle