Bratislava sits 60 kilometres downstream from Vienna on the Danube, close enough for a day trip that never feels rushed even on legs that ran a marathon the day before.
Getting There
Direct trains cover the route from Vienna in around an hour. The hydrofoil from Schwedenplatz is the more memorable option when it runs: a river approach past the Devín Castle ruins, landing near the SNP Bridge in the old town itself. April keeps the crossing far quieter than the high-summer river-cruise crowds.
The Old Town
The Slovak old town is small enough to walk completely in two unhurried hours: the Hlavné námestie (Main Square), the Primaciálny palác, and St Martin's Cathedral, where Habsburg rulers were once crowned. The Blue Church, Kostolík svätej Alžbety on Bezručova, is the one genuine architectural surprise on the walk, a 1913 Art Nouveau building in complete blue-and-white tilework that looks implausible in photographs and more so in person.
Keep It Simple
The point of Bratislava the day after a marathon is a low ceiling on activity: old town, riverside, coffee, train back. Everything costs roughly half what it does in Vienna, which makes an unhurried lunch an easy decision rather than a splurge.
Getting Back
Return trains and, when running, the hydrofoil both cover the same route back to Vienna, making Bratislava workable as a single relaxed day without an overnight commitment.