Manchester's main station is Manchester Piccadilly, though cheaper, slower trains sometimes run to the other stations. Piccadilly is about fifteen-twenty minutes walk from the Town Hall. You may want to catch the Metrolink tram (blue line on the map) to St. Peter's Square (the Altrincham or Eccles lines). This stops right behind the Town Hall (St. Peter's Square). The tram costs about £2: you can often ride it for free with your train ticket (if it states
as your destination). There are taxi ranks at Piccadilly, Oxford Road and Victoria stations.
Manchester Airport is very convenient: trains from Manchester Airport take about twenty minutes to Manchester Piccadilly and run about every twenty minutes. Taxis cost about £20, the train about £3.
Car or Bus
Good luck. There is plenty of parking: under the Novotel is probably closest. Chorlton Bus Station isn't terribly nice at night.