Since it looks like we’ll be awhile, Esra gives the accessible parts of the interior space a thorough search. Taking 20 for as long as it takes.
The long hall that you are in is a crafted stone tunnel semi circular in shape. The entrance is an illusion from the outside but clear from the inside.
The sides of the tunnel appear as smooth stone, but upon close inspection is coated with a fine coating of sand grain sized gems.
The two ends have what you assume are similar 'doors'. The one you can see that leads farther in is stone, not coated in the gems. The other is open, so you can only see the edge of it in the ground and the grooves between it and the in place floor.