When faced with the option to travel, the players must travel to Deep Chasm if there is no active location.
The chasm was long and dark, and filled with the noise of wind and rushing water and echoing stone.
–The Fellowship of the Ring
Response: When you travel to Forked Passage (before resolving the deep keyword), raise each player's threat by 2 to look at the top 2 cards of the Caves deck. Put 1 on top of the Caves deck and put the other on the bottom. Then, add Forked Passage to the victory display.
Cave Entrance gets +1 for each Dragon Sign in the victory display.
Travel: Raise each player's threat by 1.
That, of course, is the dangerous part about caves: you don't know how far they go back, sometimes, or where a passage behind may lead to, or what is waiting for you inside.