Since July 2012, a riverbus has been running in Budapest along the Danube. A river tram is equated with public transport and on weekdays it has BKK tickets. In total there are three city routes running from the Rakoczi bridge to the island of Nepsiget (No. 11, 12 and 13), and one connecting the island of Molnar with the left bank of the Danube (No. 14).
Most of the attractions of Budapest are located along the banks of the Danube, so river trips in Budapest are very popular. On the left bank is Mount Gellert with a monument to St. Gellert and the Liberation Monument, the Buda Castle with the royal palace, the church of St. Matthias and the Fisherman's Bastion. On the right bank is the Palace of Arts, Parish Church, Gresham Palace, the building of the Hungarian Parliament and more. In addition, while walking along the Danube, you can admire almost all the bridges of Budapest: Rakoczi, Petofi, Svoboda, Erzbet, Secheni Chain Bridge, Margit, Arpad (the river tram does not reach only one bridge - the Medieri).
The timetable, routes and location of stops can be viewed on the website (river trams are marked with the letter D with a wave). The duration of the walk from the starting station to the final is about 2 hours (depending on the route). You can sit and get off at any intermediate station. All stops are also marked on Google maps.
Note: I recommend taking a stop at the Boráros tér H (Petőfi híd) stop and getting off at the Jászai Mari tér (Margit híd) stop. Firstly, on this section, all three river tram routes coincide, so it’s less to wait for the next one. Secondly, along this section are the most beautiful bridges and the most important attractions. Thirdly, it is most convenient to get to these stops. Fourth, the duration is the most optimal - 50 minutes (not long, but enough to admire everyone and take pictures).