The Faerie plane is an alternate world where those of the faerie races originate. This is just the physical plane, however. On The Faerie plane exist the nature spirits, the Faeries, and Elementals. The ethereal plane can be considered a 'shadow' of the physical plane in that they closely mimic each other. The nature spirits are very powerful, since they command the forces of the elements themselves, and cannot be bound or coerced by magical means. They have their own agendas and thus are very dangerous individuals to deal with. Divided into two groups, the Seelie and Unseelie Courts, they are led by a King and a Queen, respectively.
Seelie Castle
1st Classers - Visit the merchant named Jithox at recall in Seelie Castle. To trigger him, you might need to die in Seelie Castle or just recall. When you are alive, he will speak to you. Say yes, and he will transport you to Rune.
Sidhes - Give a gold chain to the King in Seelie Castle. Gold chains can be looted from a seductive naked faerie who wanders in the courtyard.
Hellbent Mountain
Restricted to levels 61+ - enter Hellbent mountain, and use a 'word of recall' scroll (or type recall if below level 75). Then say: By the flames of Gath, deliver me from this inferno and a portal will open. Enter this portal, and walk south and east to follow the path down the slopes of Hellbent. Be careful to avoid the death trap - stick to the west side of the slopes, heading down until you can exit the area.
Gemstones
Hold and use a warp gemstone in the wilds to take you to that gemstone's location.
Non-Faeries
Visit the King in Seelie Castle or the Queen in Unseelie Castle, and they will cast you out of the Faerie Plane.