The city centre is compact and walkable. The main sights — old town churches, the central square, restaurants — are all within easy reach on foot.
The Daugavpils Fortress sits about 2km north of the centre, a 15–20 minute walk along a straightforward route, or a short and cheap taxi ride. Local buses also serve the fortress area.
Taxis are inexpensive and useful for getting between the fortress and centre, or for reaching accommodation further out. Ride-hailing apps may have limited coverage; asking your hotel to call a local taxi is reliable.
For exploring the Latgale lake district, a rental car is the most practical option — public transport reaches some villages but timetables are sparse. Car hire is available in the city.