We had friends recently stay at the Hilton near "Union Square". It didn't describe that it was basically in Tenderloin and the area was pretty shitty, and even worse at night. Had we known we would have warned them, because it's very deceiving.
The Hilton is legitimately in the Union Square area. The problem is that if you take the most obvious route to Market St. and the Moscone, that takes you right through the Tenderloin if you don't know to avoid it. (That said, I try to avoid the Hilton on O'Farrell if I can.)
