Budapest, the city that has something for everyone. My first and only time here was back in April 2019 and it's somewhere I've wanted to go back to every time.
Budapest was actually two different cities until 1873 when the cities of "Buda" and "Pest" formed one city (the city of Óbuda also joined this city as well)
The river Danube flows through the city and can be viewed from Budavári Palota (Buda Castle) which also provides amazing views of the Széchenyi Chain Bridge, which looks particularly great at night.
I would definitely putting Budapest high on your list of places to visit once restrictions are eased.