Bregenz is well connected by rail. The train station sits a few minutes' walk from the lakeside and connects directly to Vienna (around five and a half hours by express), Innsbruck (about two hours), and Zürich in Switzerland (about ninety minutes). International trains stop at Bregenz on the route between Austria and Switzerland, making it an easy combination stop on a broader trip.
The nearest significant airport is Zürich (ZRH), about ninety minutes by road or rail. Munich airport is around two hours by car. Friedrichshafen airport across the lake in Germany is closer but has more limited connections.
By road Bregenz sits on the A14 motorway, easily reached from the motorway network connecting Switzerland, Germany, and the rest of Austria. The town is compact enough that a car is not necessary once you arrive — the train station, the lake, and the old town are all within comfortable walking distance of each other.