Baden-Württemberg has a solid public transport network, though a car becomes useful if you want to explore the smaller Black Forest villages or the lake shore.
By train
The state is covered by the Baden-Württemberg-Ticket, a day pass (around €25 for the first person, plus a few euros each for additional passengers) valid on all regional trains and most buses within the state. It doesn't cover ICE or IC trains. Buy it at any DB ticket machine or online. The main rail corridors — Stuttgart to Heidelberg, Stuttgart to Freiburg via the Schwarzwaldbahn, and the Rhine Valley line down to Basel — are fast and frequent.
The Schwarzwaldbahn between Offenburg and Konstanz is one of the most scenic rail lines in Germany, looping through the forest via 37 tunnels and 163 bridges.
By bus
Regional buses cover many smaller towns not served by rail. In the Black Forest, several bus routes are included with the Baden-Württemberg-Ticket. The Freiburg region has good bus connections into the forest valleys.
By car
The autobahn network is excellent for long distances. In towns, parking is metered and increasingly restricted. Freiburg and Stuttgart have environmental zones (Umweltzone) requiring a green emissions sticker (Umweltplakette), which rental cars usually come equipped with — check before driving in.
By bike
The region is very cycle-friendly. The Bodensee-Radweg circuits Lake Constance (around 260 km, mostly flat). The Black Forest has challenging but rewarding cycling on trails and quieter roads. Bikes can be taken on regional trains with a bike ticket.