I visited the museum behind the Pavilion about 10 years ago, and seem to remember the exhibition saying that Brighton once had three mainstream theatres, of which the Theatre Royal was the only one still going (presumably they weren't counting the Gardner Arts Centre as it was only built with the university and considered the Komedia to be a fringe venue). If the Theatre Royal was one and the Hippodrome another, where was the third? Was the Gloucester originally a theatre?
Talking of the Hippodrome, I didn't know it was there until I walked down Middle Street on my way to a gig at the Brighton Centre (though there may have been a thread on here before then - the old memory is fading somewhat).
West Pier?