I try to focus on stamps with cultural relevance, that is, I avoid colourful series such as "famous operas/composers around the world". The topic of the stamp and the issuing country must have some connection.
I collect stamps of operas, opera composers, singers, houses, festivals etc., and as my collection grows I will organize it according to these sub-categories.
I thought to start this thread by posting a few stamps of opera houses / locations.
First up is a 5 mark Finnish stamp from 1930 of Olavinlinna, a 15th century castle located in Savonlinna, Finland. It houses the annual Savonlinna Opera Festival.

Next up is an aerial view from the city of Savonlinna, Olavinlinna showing prominently in the middle. This is a Finnish stamp of 1,90 marks from 1989.

Below is a series of 1, 2 and 5 Ft Hungarian stamps from 1984, released to celebrate the reopening of Hungarian State Opera House.



And finally, a Soviet stamp from 1983 celebrating the bicentennial birthday of the then Kirov Theatre of Leningrad, now Mariinsky Theatre of Saint Petersburg.

I will post more pictures sometime soon. Hope you enjoy them!