Wavering between old, abandoned factory and gentrifiable condominium complex, the Gates Rubber building doesn't appear to be a hotbed of, well, anything. At best, it's a little bit of Queens right off I-25. But for experienced spray-painters (and criminal trespassers), the place is an amusement park, art gallery and Mt. Everest all rolled into one. Because after they get past the private-property signs, chain-link fences and high red-brick walls hung with stopped clocks, this is graffiti heaven. Huge block letters dominate the upper facades; the high windows are painted backward on the inside so that their messages are legible from the street. Mountaineers, ahoy: The crowning water tower is looking awfully drab.