Update: We've moved the screenshot of the level below the fold. Click through to see it!
Players have discovered the rumoured Diablo 3 secret level only a few days after the game's release. It's called Whimsyshire, and it's a playful poke in the ribs for anyone who accused the game of being too colourful back when its art style was originally unveiled. Whimsyshire is a neon-green children's cartoon complete with rainbows and playful little happy clouds. Hooray!
The portal to Whimsyshire is a glowing rainbow crevasse that can be unlocked during Act 1 of the game, provided that you've collected the right ingredients from elsewhere. Enemies range from ponies to Cuddle Bears, but don't be fooled: it's equivalent to an Act 4 dungeon and it'll turn your fresh character into a brightly-coloured smear without a second thought.
You can find a guide to opening Whimsyshire over at Diablowiki.net . Be warned, though: the steps cover all four acts, and contain spoilers. Whimsyshire isn't going anywhere: come back when you've finished your first run through the campaign.