By TGV from Paris Montparnasse. St Brieuc is on the TGV Ouest line between Paris and Brest. There are about 10 trains a day. In some cases, you may need to change trains in Rennes. The train ride takes about 3 hours.
St Brieuc is on the N12 expressway about 90 min from Rennes. Watch out for the speed cams on the bridges.
You can transit through Roscoff, 2 h by car to the west. or Saint-Malo, 90 min to the east. Brittany Ferries runs overnight car and passenger ferries from southern English ports of Portsmouth and Plymouth.
St Brieuc has a tiny airport. The only flights landing are those from the Channel Islands, a fast but expensive way of getting here. Ryan Air flies from London Stansted and East Midlands to Dinard Pleurtuit Airport which is about 90 min to the east.
The centre is compact and walkable. There is really no need to get a bus unless you are staying in the suburbs.
The local bus network (TUB) serves the St Brieuc urban area. This is similar in scope to any equivalent sized French city. In the region a patchy network of buses exists (Bus D'Armor).
The service is very irregular.
Saint Brieuc doesn't offer the same tourist draws as other historic towns in the area such as Dinan and Saint Malo. However it's a great place to stroll around and observe a fairly typical working French town. It does have a lively arts scene. During the summer you can enjoy a lot of free music. Talent from all over France descends on the town. Summer music festivals such as les Nocturnes and L'Autour du Blues (at Binic) are big pulls.
The city is blessed with a series of valleys. Two rivers meet (Gouët and Gouédic) here before they empty into the sea. Very scenic views on the approach to St Brieuc on the N12.
Your usual Breton souvenirs. St Brieuc is not full of tourist trinkets (mercifully) It's more your regular French large town. Most of the consumables you'd find in any town are available.
Celtic art gift shops have sprung up in the past 5 years. Cufflinks with triskell motifs make good presents. The Breton flag (Gwen ha du) also looks mean on a T-shirt.
Any of the places on Place du Chai. The most lively place in St Brieuc.
There's Youth Hostel about 2.5 km out of town (Manoir de la ville guyomard).
If that doesn't float your boat there are numerous 2 star hotels in the immediate city centre.
Out of town at Langueux (new commercial development 2 clicks east of town on the N12). There are the regular French motel type chains. Formule 1 and Ibis (Yffiniac) are represented there.