Brighton Station, Trafalgar Street entrances
Brighton Station had two direct pedestrian entrances on Trafalgar Street, an "original" (early 1840s, maybe 1841, 1842 or thereabouts) entrance passageway that is under Trafalgar Street Bridge, and a second entrance opposite the Prince Albert Pub, built when the station was extended, which is now half-hidden behind a low-walled electrical transformer.
The first Trafalgar Street entrance
The original pedestrian entrance to Brighton Station from Trafalgar Street is still visible under Trafalgar Street Bridge, as the rectangular "arch" with a white flanking surround and bevels on its upper corners.
The entrance led to a set of stairs that went up to the station concourse. The place where the entrance emerged is still visible from the station's public area, and sometimes it's possible to peek through the cracks of the metal shutters closing it off to see a glimpse of a gloomy set of stairs.
There was some talk of possibly reopening the entrance as part of the ~2013 station redevelopment programme, but the arguments seem to have been insufficiently compelling, because it didn't happen (possibly partly because the passageway is already so close to the main frontage of the station anyway).
The second Trafalgar Street entrance
When the station was extended Eastward over the top of the Cab Road, the management took the opportunity to build an additional pedestrian entrance on the station building's new corner, again facing Trafalgar Street. This entrance goes to a more involved stairwell that comes out in the corner of the current cab area, where it's hidden behind the cycle racks by the station's Travel Centre.
This would have been a very useful entrance to reopen in ~2013 given that the corner is so far from the other existing entrances, but unfortunately somebody in the past had decided to use the space in front of it to situate a large electrical transformer (right in front of the door's "do not obstruct" sign!), and finding a new location for the transformer and relocating it would probably have have been expensive.