undersurface

The nest was some forty feet from the ground, on the undersurface of a shelf of rock.

The undersurface, originally a bright red, turns brown and runs in every direction into a mass of dark stalactites.

There had been a lot of that at first, in the early days before the transfer to undersurface was complete.

You couldn't expect to have everything perfect, living undersurface, with an artificial sun and artificial food.

Until our families can come up from undersurface, it's going to be pretty lonesome, but we'll have to manage.