The Phlegethon of Unrelatable Nightmares Multi-cache

Deep within the misted hills of refulgent Solvay it is whispered of a cache so unspeakable, so riddled with the scrofulous horrifying befoulment of lurking fears that those who have sought its obsequious mysteries have returned gibbering with madness, or have never even returned at all! The first stage lies within the mouldering stygian orifice you see before you, 7 "beams" into the squamous maw of DOOM!

...but enough of that, here's the History Lesson. Built in 1908, this tunnel runs thruough Terry Road Hill, and was part of the "bucket line" (think of a modern-day ski lift) that transported crushed limestone and other materials between Split Rock Quarry in Fairmount and the Semet-Solvay Company, where it was turned into soda ash. It is one of the last 3 remaining "big" structures of the Split Rock era, which ended with the infamous 1918 TNT disaster. The other 2 are the old quarry's Rock Crusher and "Frankenstien's Castle", the only remaining brick guardtower.