From Runescape - Wiki on Neoseeker

Mini-games are located throughout Runescape. Most are available to accounts with members (P2p) status, although a few can be found in free to play worlds (f2p). Some mini-games are considered safe, where you do not lose your items if you die or if it is not possible to die in that area due to lack of things to attack.

Mini games are often sought after for clan and community events. You will find some worlds are "themed", which means you can usually expect that mini game to be highly populated on that world. Mini games offer many rewards, from powerful barrows and 3rd Age armour, too more fun items like new outfits. Most mini games also offer a form of gaining experience whether its combat or non-combat skill oriented, and can generally be a lot of fun with friends.

Mini-games