Caved in Ruin

A few yards away from the place the bridge dumped the party is a treasure tucked up against the cliff.  It's easy to overlook if one is not paying attention, covered in vegitation and obscured by massive boulders as it is.
At first all you can see is a pillar, massive in size, towering at a intimidating 20 feet above you.  It's carved out of a slab of cream colored stone, and at first glance it appears to be cracked and missing peices.  But if you take a step back you can see that the cracks are in fact, intricate designs.  Clear and geometric in design, the edges of these designs look dangerously sharp and you make a mental note not to run your hand over any of those edges for fear of slashing your palm clean open.
It's only as you stand back and observe this pillar from a distance that you realize that it isn't just a single pillar, and it is infact, an archway built into the side of the cliff.  A second, smaller archway, just as sharp and graceful, sits atop the first, although this one is not filled with boulders bigger than you are tall, but a pearlescent green glass ([dc: 25, nature] that's actually a slab of thin opal that's been turned into a window of sorts) that's been shattered and left in large chunks hanging from the frame.
The second half of the larger archway has been mostly obscured by the rocks that fill the entrance, large chuncks of the second pillar lay scattered about the grass around you.
The team can attempt to clear away the debree (dc 15: investigation/perception) There is no way for you to clear the entrance, every boulder removed just revieles another one and it would be exhaustive (time wise and personally), to try as you don't know how deep the cave in goes.

Purpose / Function

It appears to be a doorway into a structure built into the cliff face.  The way deeper is blocked by a cave in.  There's no telling how deep this cave in goes, or if this is the only surviving peice of the structure.

RUINED STRUCTURE
unknown

Founding Date

unknown

Type

Architectural Element, Entrance / Entryway