i was curious.

i don't know whether the hermit makes its own shell or not, but i suspect that it does. how bout this:
SEA HERMIT LAIR
A sea hermit's home is its gigantic, majestic shell. This squat, conical structure is roughly 20 feet in diameter at its base (60 feet in circumference), and rises up in a spiral 30 feet high. The exterior of the shell is usually white with deep blue and red markings. The shell is one foot thick, with a hardness of 6? and 75 hp per foot of thickness.
The interior is no less impressive. The first 40 feet of the shell, as it wraps around the first curve, is where the sea hermit in its natural form fits. Past this, the shell has been reshaped to form archways, stairs, and rooms, including a laboratory and cells for prisoners. A few secret doors may be installed, perhaps some ending in traps for overcurious guests; those often involve spring-loaded tridents tipped with the poison of an exotic fish. In some areas, the overlapping spirals bend some of the ceilings, making the overall architecture lack the hard edges and corners to which most races are accustomed. In areas of sharp upward slope, the sea hermit has formed a polished stairway from the shell's glossy mother-of-pearl interior. The effect is quite beautiful.
When posing as a humanoid, a sea hermit will decorate the lower portion of its shell to add to the camouflage. It clutters the area with driftwoods and minor implements, to suggest a craft workshop or junk storage area and avoid suspicion.
If a sea hermit is killed, its shell can make an excellent shelter and even a small base of operations. One persistent rumor even suggests that a wizard has transformed one of these great shells into something like a
Daern's instant fortress.