Outside the Nature altar.
The Nature altar may be found northeast of Shilo Village. It is used to craft nature runes from pure essence, providing 9 Runecraft experience.
location of the nature altar
As with most other runecrafting altars, it can be accessed via the Abyss. Players can also enter its ruins by using a nature talisman or a nature tiara; players can teleport close by via fairy ring code C-K-R.
The maximum likely limit for crafting nature runes in one visit is 108. This would be achieved by having 91 Runecraft, giving a 2x bonus, and carrying 54 essence to craft (24 in the normal inventory along with 30 in the 4 sizes of pouches. The maximum possible experience is 486 obtained while doing the above.
A nature tiara may be created at this altar by having a nature talisman and a normal tiara in your inventory. The player must use the tiara on the altar. Doing so gives 45 Runecraft experience.