We’ve mentioned Europeana before on the Red Dot but it’s certainly worth mentioning again – it’s a site that brings together digital content (all media!) from all aspects of European culture: museums, archives, libraries, and historic sites. They’ve launched an app called the Europeana Open Culture app (download it here), which showcases some of their partner collections. They’ve got a great blog post that illustrates some of the collections’ riches, using the Rijksmuseum’s public domain works as examples. Whether you explore it using the app, or the website, you are entering a vast world of content.
There are some website search tips here, and browsing via the exhibitions page is a wonderful way to explore by subject or theme.