TopoSym2021 [http://www.toposym.cz]The 5-yearly Topolopy Conference TopoSym2021 will take place from July 26 to 30 2021 in Prague, and I hope that many of you see this as an excellent opportunity to visit both cities.
Travel between Vienna and Prague is not complicated and there are multiple ways. There are multiple flights, but cheaper are the train and bus.
The fast train between Wien Hauptbahnhof and Prague Main Station takes slightly over four hours, and there is one every hour or two hours. Prices range from 20 to 60 euro one way (depending on time of booking and popularity of time. The Austrian Railway site is https://www.oebb.at.
The German Railway site https://www.bahn.de is in general the best for train-information within Europe, but may not have detail price information in neighbouring countries.
Tickets Prag-Vienna bought in the Czech Republic may turn out to be cheaper: https://www.cd.cz
Bus-lines are also frequent from Vienna (Edberg or Hauptbahnhof) to Prague Bus station (behind the Main Station). One way it takes between 4 and 5 hours, and costs between 10 and 20 Euro. Their buses have on-board toilets (narrow but doable, and they have aoccsional stops at a road restaurant).
Currently, most lines are offered by Flixbus: https://www.flixbus.at (Austrian site/ other countries have their own Flixbus site).