Preston bus station is not only hideous to look at, it isn't fit for purpose and is downright dangerous for bus users.
There are two winding subway tunnels to get out of the station into the city centre, both tunnels are poorly lit, have rarely working CCTV and are usually full of alcoholic beggars and narky buskers. You often find gangs of chavs drinking copious amounts of alcohol in them as well. If you don't want to exit through these tunnels you can try to 'escape' over the bus apron, this is against the rules/advice of the bus station and many have been killed or injured over the years when doing this.