I just read that the line between Vienna & Bratislava Hlavna station is to remain closed until approximately July 2025. It was originally expected to reopen Dec. 2024.
So, those planning a day trip from Vienna to Bratislava via train will need to use the Bratislava Petrzalka station on the west side of the river.
https://www.seat61.com/trains-and-routes/vienna-to-bratislava-by-train.htm
Buses run from the front of the train station to Bratislava too. Check into them. It's just about 39 miles.
Train tickets to Bratislva Petržalka are good for riding on bus 93 to the city center.
Personally, I find the bus to be easier as it stops in Bratislava city center at the UFO bridge (Brastislava Most SNP). You easily catch the bus in Vienna at Erdberg, a stop on the U3 subway line, or from the bus station at the Main Train Station (Hauptbahnhof). I like to use Flixbus. The ride takes about an hour and costs about 10 Euro pp.
Personally, I find going by train more comfortable. Incidentally, I try to avoid Flixbus, because they treat (and pay) their drivers badly to minimize costs. Otherwise they could not offer so low fares. (The same holds for RyanAir.)
