Rousse is located on the South bank of the Danube, across from the Romanian city of Giurgiu. By road, the city is about 200 km from Varna and 300 km from Sofia. From Romania, a bridge connects Ruse to Giurgiu, serving as the westernmost land connection between the two countries (although ferries operate between other cities, and a new bridge is under construction at Vidin). If you intend to cross the border from Giurgiu, an 8 ? (~15.5 Bulgarian Leva, ~28 Romanian Lei) crossing tax applies each way.
The closest international airport is 75 km north, in Bucharest, in neighboring Romania - a shuttle bus connects the airport to the city once a day. Alternative airports are Sofia and Varna.
The city is well served by railroads, with multiple connections to Sofia and Varna, but also to Bucharest (2x daily, but note that the train is rather expensive - 25 ?, and very slow, taking about 3 hours for the journey), Budapest, Kyiv, Moscow, Athens and Istanbul. The train station is at the southern end of Borisova Avenue, near the Rousse TV tower.
Buses also link Rousse to the rest of Bulgaria (different frequencies daily), places in Greece (daily) and to Giurgiu (hourly) and Bucharest (twice daily). The bus depot is located next to the train station.
Danube cruises generally call at Rousse.