A fairly large industrial town (but not a city) on Teesside (south of the River Tees) in the Northeast of England.
Whilst most of its industry comprises large chemical plants owned by the likes of ICI, Tioxide, DuPont etc, Middlesbrough is allegedly one of the only places in Europe with two oil refineries within walking distance of the town centre. Consequently, the air in Middlesbrough has a special taste to it which inhabitants of other industrial towns will know all too well.
Other things to note about Middlesbrough include:
People from Middlesbrough have a distinct Northeast accent (you may have heard Bob Mortimer, Roy Chubby Brown or Chris Rea) but they are definitely not Geordie. Be careful when talking to people from Middlesbrough, Sunderland and Newcastle: they all have separate identities and are willing to reinforce this with violence if necessary.