In short
Bratislava touches both Austria and Hungary: it is the only capital in the world that does. Vienna is an hour away by train, and a boat runs down the Danube between the two.
The historic centre is tiny and can be walked in two hours. The city works as a base, not as a multi-day destination.
What it really costs
Slovakia is in the eurozone and Bratislava costs about a third less than Vienna, sixty kilometres away. Plenty of Viennese come here to shop and to see the dentist.
The ratio reverses for anyone arriving from the east: this is the most expensive city in Slovakia, well above Košice or the rest of the country.
What nobody tells you
Vienna's proximity defines the city: many people sleep here and work on the other side of the border. The regional train links the two in an hour for a few euros.
Petržalka, on the far bank, is one of central Europe's largest housing-block estates, built in the seventies. It is a part of the city no circuit shows, and one resident in three lives there.
The castle dominates everything but the interior is a nineteen-fifties reconstruction. The view from the esplanade, though, is free.