It is called air altar. It is a little south of the road from Varrock to the Barbarian Village (i.e., west of Varrock). If you have trouble finding it, take an air talisman with you - it has an option to show you the direction. To craft runes, you need either an air talisman or an air tiara anyway.
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The air altar moved from its original location it is now located between the Barbarian Village and Varrock, use "Locate" option on your air talisman to get it's exact spot.
Exit the gates north of Varrock, turn right and head down until you find it.
you have to blow air on the leaf.
It's just to the west of varrock.
It's very close to varrock. Type it in on your map and you will see. Right off the wilderness line/wall.