Tosca in Vienna, booking opens on May 5
For the performances in September online booking opens four months ahead. Very good news as normally we can just apply and hope we get tickets. Which doesn't happen all the time.
Top priced tickets for Tosca at Staatsoper Vienna on September 5, 8, 11 and 15, starring Angela Gheorghiu, Marcelo Alvarez and Zeljko Lucic under Marco Armiliato's baton. An all star cast that deservers the fight for a good ticket.
So, if you want to go on September 5, the online booking opens on May 5. If you want to go on September 8, the online booking opens on May 8. And so on.
If you don't get a ticket, no worries. All you need is lots of patience to stand in the daily queue, maybe the most demanding daily queue at any opera house. As you know, once you get in line early in the morning you can't leave it for more than 15 minutes. The good part is that you can have some of the best standing seats in the house for only 5 euro or so. Been there, done that. Exhausting but rewarding. There are about 400 standing tickets every day, so there's plenty of space for everybody.
As hint, there's a very good view (and sound) from the gallery and the tickets are cheaper. I once tried the gallery standing tickets. Not that bad, but there's a side view which might be uncomfortable. Still, you're inside the opera house.
If you intend to attend La Boheme in December or Adriana Lecouvreur in March/April, then preorder tickets. The online booking opens only two months before each performance and there are high chances that you'll find only the most expensive tickets.