Crystal Tokens are portal keys that are used to access the Temple of Silver. One may get there by dropping a token on the island temple known to Crausaar. To leave the Temple of Silver and return to the surface, one must drop another token from within.
Although the Knights of Silver have many tokens, so far only 8 have been given away in recent history, to The Hidden Vale. 4 of these tokens have been used by the Vale. 2 other tokens were offered to King N'eroth, in the hopes that Mirith would enter into an alliance with the Knights. N'eroth took the tokens at a dinner party on Day 203 of the Blue Moon, Year 439, and left to consult with his mages. He has not been seen since that day, and it is unclear whether he used the tokens or not.