Bregenzer Festspiele: the opera Carmen
 

Hello all, my husband and I have got tickets to the opera Carmen at the famous Bregenzer Festspiele this August. We have a hotel reservation for two nights in Bregenz.
In preparation for this event we visited Bregenz last October on our way to Italy. Aside from it's stunning location on the shore of Lake Constanz we did not discover any 'not to be missed' sights. Am I wrong? Are there perhaps any 'must see' undiscovered gems in the area? We plan to travel by train from Amsterdam, the Netherlands to Friedrichshafen where we will spend the weekend with friends. From there we plan to take the ferry across the lake to Bregenz. Any suggestions are most welcome!

You may check (google):
Friedrichshafen:
Dornier aviation and aerospace museum
Zeppelin Museum
Meersburg: castle
Unteruhldingen: Celtic Lake Dwellings
Mainau Island: subtropical gardens
St. Gallen: medieval city center with cathedral and library (Unesco site)
Pfaender, Hoher Kasten, Saentis: viewpoints accessible by gondolas.

Low cost airline fares Amsterdam - Zurich or Stuttgart start around 60 EUR (Transavia, Easyjet, Eurowings)
Zurich airport is 1 hr by train from Lake Constance (trains every 30 min)
Stuttgart airport is 3 hrs by train from Lake Constance

neckervd has already listed some of the top sights of the area. Let me add Lindau with its old town on an island in the lake, and the medieval abbey churches of Reichenau (World Heritage site). None of these actually qualifies as "undiscovered"...

Dear Neckervd and Quokka, due to serious family circumstances at the beginning of March my thoughts where elsewhere and I was not in the position to answer to thank you for your suggestions.

August is drawing near and we are very much looking forward to our trip to Austria.
FYI: we have found an alternative way to travel which is a) eco friendly
and b) very affordable. We'll take a direct train from Amsterdam to Bregenz, (8 hours) first class round trip for €250.

Perfect solution: both changes at the same platform!