It's the main port in Scotland for serving Northern Ireland, thus there is a great deal of through traffic. Stranraer sits on the shores of the sheltered Loch Ryan, located on the Rhinns of Galloway, which is a windswept peninsula that is shaped like a pick-axe head on the end of the coast of Solway. The town has a population of 10,700, many of which work for the port's business.
However, some people may find themselves with time to kill in Stranraer. In that case, you can always head for the Castle of St John, which is a four-story tower house which now lays as a ruin, standing on the main street only a block inland from the front of the harbour. It is basically the one specific attraction in the town. If that doesn't use up your time, there is a brief foray into the local history of the town and an exhibition about local Arctic explorer John Ross who discovered the North Pole on offer at the Stranraer Museum which can be found at the local town hall. There is also a selection of Hotels in the town and birdwatching is apparently recommended.
The East Pier of the Stena Line Ferry terminal is where the boats leave for Belfast from and there is a train station right next to the terminal. The bus station is on Port Rodie. The West Pier is where the fast HSS Catamarans leave for Belfast from. It is the other side of the harbour from the East pier obviously, but it's still important to know which is which. Should you be taking the P&O Irish Sea ferry back and forth from Larne you will be going to the port of Cairnryan, which is 5 miles north of Stranraer. However, you should note that there are only infrequent bus services from Cairnryan to Stranraer and the buses are not integrated with the times of the ferries.
You can get to Stranraer via the 920 National Express bus from London, which then goes onto Belfast via ferry. This is an overnight ferry. Glasgow is 3 hours away through Stagecoach Western and Ayr is 2 hours away. Trains run to Glasgow (2 hours) and Ayr (1hr and 20 mins).
Stranraer has a tourist information centre which is at 28 Harbour Street in the town. This is normally open from around 9:30 am to around 5:30pm. The telephone number is 702595.