It’s easy to waste a lot of time looking at silly videos on the Web, but if you want to sharpen your brain cells, there are also some hidden gems – especially educational programming. If you’ve got time  to kill at the gym or winding down before bed, while not learn something with a nice documentary? You don’t even have to have to flip around the TV or spend valuable time rooting around online trying to fine them, because several sites and apps that do the work for you.

For example, the PBS app lets you stream hundreds of public-television programs including NOVA, American Masters, Time Scanners, American Experience and plenty of standalone documentaries produced by PBS member stations. (You may have to register with the PBS site to use the app, but it’s free.) You can get the app for iPhone, iPad, Amazon Kindle and a number of set-top boxes like Roku and Apple TV. While a bonafide straight-up Android app isn’t available at the moment, you can stream videos from the PBS website on Android devices or on the desktop. (PBS has acknowledged ground to make up in Android app development, but it’s working on it — for the younger set, the PBS Kids app is now out for Android, iOS and Kindle.)

For short clips about a particular aspect of American history or culture, visit the website of Smithsonian magazine to see videos detailing things like the history of the electric guitar or the origin of Wonder Woman. You can find more clips and full-length episodes of programs on the Smithsonian Channel’s site. The Smithsonian Channel also has its own mobile apps for Android and iOS and has begun to show up on some streamers — again Roku, Apple TV, that sort of thing.

For space nerds who want to keep up with events, the NASA Television channel and other multimedia content can be streamed from the NASA  website or its various mobile  apps.

Documentaries can also be found where you might expect them. The Internet Archive has a video section with an area devoted to cultural and academic films, as well as collections devoted to movies and classic TV. The free version of Hulu has some ad-supported documentaries as well.

For modern history buffs, the British Pathé film archive has 90,000 historic clips and a YouTube channel. Keep in mind, not everything is available at full-length to watch for free, but there’s some amazing bits of 20^th century history to peek at, including news footage from World War I.

Serious fans of cultural, historical and nature documentaries can indulge themselves and one of the many sites out there devoted to categorizing YouTube video by topic. TopDocumentaryFilms.com is one great place to start and here, you can find things like Simon Schama’s 15-part A History of Britain miniseries, the Planet Ocean nature film or a biography of Aaron Swartz.

Similar sites like 1001 Documentaries or DocumentaryAddict.com can also help sat your craving for both streaming video and learning something in the process. And when your brain is all stuffed with new things and you need a break from the mental exercise, you can always cool down with a few cat videos.