Eiken is probably the most infamous loop in Yggdrasil. It was the only universe besides the Hub to survive the original damage to Yggdrasil and the Crash entirely unharmed, and is the most commonly used punishment loop. It is run by the admin Aphrodite, and is her only loop as she does not like hard work.
The setting of Eiken is a mostly normal high school, except that females have far larger breasts than exist in the Hub. It is commonly thought of as incredibly bland. Twilight Sparkle's guide for new loopers describes it as "Wish fulfillment for the protagonist, and you are not the protagonist."