When you first get to Relic Castle you're pretty limited. You only have the first floor. So, progress onwards in the game until you can actually go through it.
My suggestion is beating the Elite Four and then coming back.
You sell it to the relic maniac, in the Undella mansion.
at the end of it
The Relic Statues in both Pokemon Black and White are acually Darmanitans. But these Darmanitans have the secret ability Zen Mode which will change it's form and stats when its HP is low. You can wake them up with the RareCandyBar that Prof. Juniper will give you when you enter.
Zekrom (Pokemon White) and Reshiram (Pokemon Black).
Nimbasa City, Relic Castle, Black CityB, Pickup, dust clouds, held by wildSolrockNimbasa City, Relic Castle. buy from Black City (only in pokemon black), pickup, dust clouds from caves, and held by wild solrock in giant chasm
It can be found in the Relic Castle in Pokemon Black Or White
it is in the desert near relic castle
At the desert resort
You sell it to the relic maniac, in the Undella mansion.
With a sun stone. a Sun Stone can be obtained in Nimbasa City and Relic Castle.
in the desert resort
In relic castle
at the end of it
fossil in relic castle
At one point in the plot, you will be told to go there. Only then will he move and allow you access.
Route 14, route 18, the dreamyard, relic castle, the cold storage, and the charge stone cave
Yamask can be found in the Relic Castle.