I'm in the Dark Forest and have enetered a building with guardians either side (show up as friendly) and an empty holy grail on a table/altar in front of me. I got a warning message but can't pick up the grail.

What do I need to do?

On a minor matter, I cleared out the Imp's Castle but couldn't find the teleporter. Tough fights by the way, barely survived with my lvl 26 warrior (had to use my alternate sword with Frost 2 for the two boss fightd).

Thank you.