Giessen is a small city and the main sights are walkable from the centre. The Liebig Museum, Mathematikum, Old Castle, and the university campus all lie within about 20 minutes' walking distance of one another. The botanical garden is on the western edge of the campus, also reachable on foot.
The city has a local bus network (Stadtbus Gießen) that covers outlying districts, but for most visitors it is not necessary. Cycling is practical and popular — the flat terrain along the Lahn makes it easy, and bike hire is available from several rental points near the station. The Akademischer Forstgarten on the Schiffenberg hill is the main destination that genuinely benefits from a bike or bus, as it sits about 3 km south-east of the centre.
Taxis are available at the main station and can be called by phone or app. The city is compact enough that taxi fares within the centre are modest.