The Illusion Lab created a fun illusion video that can cause some serious hallucinogenic effects just from watching the video. It only lasts for a little while, but you'll definitely feel as if the world around you is alive like you've never seen it before.
All you have to do is watch the video (full screen heightens the effect) and stare at the centre (reciting each letter that pops up makes it easy to focus). When the video is done, look away and the world starts oozing around you.
Don't watch the video if you're prone to seizures though!