Cosmic rune

The cosmic rune is used for enchanting jewellery, such as rings and amulets into something that has an effect when worn. For example, when a diamond ring is enchanted, a player will obtain a ring of life, which instantly teleports the wearer to the player's spawn point if the wearer's hitpoints drop below 1/10 of the full amount. Cosmic runes are also used for the Lunar spells NPC contact, Cure Me and Cure Group. They can be made through the Runecrafting skill at level 27 for 8 experience per pure essence.

Cosmic rune spawn
There is a spawn of 3 cosmic runes in the Ice Plateau at the far northwest corner of the free-to-play Wilderness, guarded by level 53 Ice Giants, and level 57 Ice Warriors.



Drops
What is considered the easiest way to obtain free cosmic runes is to kill Dark Wizards (found just south of Draynor and just south of Varrock), who occasionally drop pairs of cosmic runes.

Trade
Cosmics are a slow trade item, as enchanting is not a commonly used spell, so a player may find that other players sell them to a general store - for some reason, most likely due to its proximity to a large group of Dark Wizard spawns, Varrock seems to be popular - some of the sewer dungeon monsters (e.g. Moss Giants) are rune droppers.