Photo by Ken Sakamoto, Star-Bulletin

It can only be seen driving Kailua-bound in Nuuanu on Pali Highway. Queen Emma Summer Palace and Nuuanu Valley Park passes on your right, the Board of Water Supply plant nursery passes on your left, capped by an electrical substation, and - WatDat? - some sort of ancient ruins, rearing grayly out of the jungle banyans like a brontosaurus. Driving town-bound, forget it. It's invisible.

It's reachable by a short hike around the electrical station. (Go to the right, not the left, despite what your eyes tell you. That impassible chain-link fence only extends a few feet into the jungle, and can be skirted.) Watch your feet: the area is apparently a hang-out for Nuuanu ne'er-do-wells, and beer bottles, syringes and latex novelty items litter the ground. If you're lucky, you'll trip over someone sleeping it off.

The building itself is large and grand, or at least it was at some point. The roof is gone, as is the Diamond Head wall, which toppled in an east-bound direction long ago.

Banyans have taken over the massive outer walls, and probably support the building.

What is it? The Board of Water Supply - it's their property but the nursery apparently leases it to the Department of Transportation - isn't sure. The State Historic Preservation Office has little to offer either. Large, riveted pipes run through the property, and there are water outfalls on the Ewa side of the structure. These are important clues. The best guess among preservationists is that the building was a water pumping station or electrical plant, built more than 100 years ago.