The Tweenoks in Athena's dream are guarding the El Cairo key. To get the key, you'll need to pass the Tweenoks. These are two large and dangerous trees that the sheep warns about. They are found north of the sheep.
To pass the Tweenoks:
Go to Peeboo's dream and find the Giggle Bell. Equip it in Erin's left hand to pass the Tweenoks.