Can always check the backlog option, but if it's what I'm thinking of, it's the stairs behind the Bandit Leader boss that leads down in to the caverns where some stronger bandits are, including Darry and Barry. If you've accessed the shortcut it should be accessible from a house on the west of Trademond. If you haven't beaten the Bandit Leader boss, no worries, you can sneak around him using the other tunnel on the east side of the southern part of the forest.