Do you have enough gold? May be a stupid question, but I had to go back to earlier levels to acquire enough to proceed, I had somehow missed some, check all previous maps to verify. Outside of that im not too sure, sorry
edit: so just looked at mine, are you talking about the area directly to the right? If so, in that level, the mimblesnits you have to take the BLUE ARROW route. This will unlock that area. If it's the one your referring too.