My postcard of the Sun Theatre, in Yarraville, a suburb of Melbourne, Australia, isn't very old, but it has an interesting history. You can watch it being painted on an iPad by the artist, Greg Ure:

https://www.youtube.com/watch?v=SCNnnNiQKNE

(Cologne, Germany)

Cabaret and variety theatres:
“Willkommen, Bienvenue,Welcome...“ Politische Revue – Kabarett – Varieté in Köln 1928 –1938
http://www.museenkoeln.de/ausstellungen/nsd_0802_kabarett/

-Note: the morons responsible for the Cologne museums have removed this useful resource from the web (not found on 24 July 2018) -

Cinemas:
Köln im Film
http://www.koeln-im-film.de/kinos.html

A comprehensive and richly illustrated site on ancient Greek and Roman theatres (in German only):

http://www.theatrum.de/

There is also a sister site on amphitheatres: http://amphi-theatrum.de/

A comprehensive database of performance history and theatre venues in Australia:

https://www.ausstage.edu.au/

I added links to this database from all my pages on Australian theatres (where applicable).

A 1906 card sent from Regensburg to Santa Monica (California) is perhaps the one postcard in my collection that holds the most incredible wealth of pictorial information. It's the first card on the Regensburg: Stadttheater page.





At first glance the card may seem quite unsuspicious, but since it is mounted on light wood that is almost 5 mm thick , it surely stands out from any stack of postcards. With one Bavarian and no less than six American red stamps the address side it is also quite impressive.

In the middle of the picture side, there is a little leporello that can be taken out. Folded out, it is 176 cm long and contains photographed portraits of 44 members of the ensemble of Theater Regensburg.

This image shows them arranged in groups of six:



For the single portraits, see a new Wikimedia Commons category.

Scanning the card and its leporello also helped to illustrate some Wikidata items and three German Wikipeda articles:

https://de.wikipedia.org/wiki/Fritz_Cortolezis
https://de.wikipedia.org/wiki/Max_Jungk
https://de.wikipedia.org/wiki/Toni_von_Bukovics

Most names of the portraited ladies and gentlemen can be found in the "Neuer Theater-Almanach" of 1906 that is available at the Internet Archive:

https://archive.org/stream/deutschesbhnen1906genouoft#page/516/mode/2up

While all ensemble members of 1906 have passed away long ago, the theatre itself is still alive and kicking:

http://www.theater-regensburg.de/

Too many to be listed here, actually.

For a start, have a look at the cards from Albania, Angola, Australia, Barbados, Bosnia, El Salvador, Haiti, India, Indonesia, Madagascar, Montenegro, Oman, Papua New Guinea. Plus, the new opera houses of Oslo (Norway) and Göteborg (Sweden) finally got their pages.

I also added lots of cards from Germany, notably from Heidelberg, Hof, Kassel, Köln, Mainz, München (Gasteig), Münster, Neuburg, Norderney, Putbus, Rathenow, Ravensburg, Rüsselsheim, Schwetzingen, Sindelfingen, Sommerhausen, Stuttgart (Wilhelma), Trossingen, Walsrode, Weingarten, Wolfsburg, Worms, Würzburg.