You walk onwards, and as you do, the corridor you're in gets brighter. Eventually, you walk into another hallway, stretching out perpendicular to the first. The side of the hallway on the same side as the corridor you just emerged from is covered in the same solid stone, moss, and glowing cracks as the corridor you just emerged from. The side facing you, on the other hand, appears to be made mostly of open arches, letting in a good deal of natural light.
To the left the corridor appears to head down, and to the right it appears to head up. Looking out through the arches, you're pretty sure the corridor wraps around like a giant spiral, forming a bowl-like enclosure. You appear to be half-way up.