There are many ways to get to Liverpool by road, rail, air, sea, camel… ok maybe not camel but you never know. Since it's a Bank Holiday Weekend (public holiday) I advise booking as early as possible to get the best deals.
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Liverpool Lime St station is right in the heart of the city. You can get trains to here from anywhere in the UK:
Liverpool has good motorway links to all over the country if you want to travel by car. Check out the official Visit Liverpool site for a full guide.
“From the M6 the city is easily reached via the M58, M56 and M62 motorways. Liverpool city centre is approximately 45 minutes' drive from Chester, Manchester and North Wales.” - Visit Liverpool.
National Express also run cheap coach services to their station in town from all over the country. Worth considering.
Liverpool John Lennon Airport has grown massively in the last 5 years, you can fly to almost anywhere in Europe direct. There is also Manchester Airport for visitors from further afield. It's less than an hour by bus/car or train to Liverpool. For visitors from mainland Europe budget airlines seem to have the best deals, Ryanair and Easyjet offer services to Liverpool.
For visitors from Ireland getting a ferry to Liverpool is a great option. The city was built for it's location on the sea and is still a major shipping hub.
See the information on the Visit Liverpool site.