The Elemental Barrier surrounds the Garden of the Gods and prevents entry.
The Elemental Barrier is a combination of all five elements. Earth and Air joined to form a sandstorm. Cold and Water joined to form hailstones. Fire and Sand joined to form glass, glass plus hail turned into 50-pound death-balls caught up in a cyclone-strength gale that loops about the caldera, although illusion magic hides it from view unless you are within a few feet of it. It bars entry to all who don't know the passphrase: "I, a child of the Elements, would Enter."
Its a wall of death... that is its ability.
Level 25 Hazard.
Its 20-feet thick. When you enter a square or start your turn in a square, make a DC26 reflex check. If you do not succeed, take 4d10+9 damage and make a DC26 fortitude check. On a failure, you are slid back one square in the direction you came (no rolls).