I'm a fan of the Wroclaw opera house. Wroclaw is a city in southern Poland and is completely amazing (but I'm biased.) I found some pics: http://www.ashra.com/pics/photos/wroc01.jpg
The problem with the Claw is that it isn't a well known city outside of Poland. But it's a great city with lots of rivers, bridges, and the anonymous nature of the city might work for you.
Wroclaw Opera
http://www.ashra.com/pics/photos/wroc01.jpg
http://www.optocore.com/pics/service/pictures/1_OperaHouseWroclawIMG_3576.JPG
http://images.google.com/imgres?imgurl=http://a248.e.akamai.net/f/248/1229/1d/images.world66.com/th/e_/op/the_opera_house_gallerythumb&imgrefurl=http://www.world66.com/europe/poland/wroclaw/lib/gallery&h=139&w=185&sz=15&hl=en&start=12&um=1&tbnid=uO9gC4lLWEMI7M:&tbnh=77&tbnw=102&prev=/images%3Fq%3Dwroclaw%2Bopera%2Bhouse%26svnum%3D10%26um%3D1%26hl%3Den%26rls%3DGGLG,GGLG:2005-45,GGLG:en%26sa%3DN
Or, if you want a smaller venue, you can try the university's theater, but it's quite small:
http://www.hispaniaclasica.com/Imagenes/orquesta_leopldinum.JPG
The problem with the Claw is that it isn't a well known city outside of Poland. But it's a great city with lots of rivers, bridges, and the anonymous nature of the city might work for you.