Underdark
The side passage is very rough and irregular, much like the rest of the passageways you've been seeing in the Underdark. You are forced to walk single file. You proceed roughly 20 feet, and the passage begins to bend to the west, toward the larger cavern ahead. There is also a side passage off of the side passage that goes to the east, and shortly after passing that you come into a larger space (but still pretty small and cramped) that is roughly 15 feet by 25 feet. There is another passage in the wall you emerged from that leads back in the direction from which you came. 'there is also a very narrow (3 feet) passage in the western wall that leads in the direction in which your stated aim lies.
[OOC: Sorry guys, this thing does not lend itself well to mapping. If we need a diagram for tactical purposes, I'll cobble something together then. Otherwise, please bear with me?]