This sounds like a fantasy topic. My specialty :)
A group of people stumble upon ancient ruins far away from civilisation. In it is an entire race (elves), except everyone is asleep. One of the group is able to wake all of them up. It turns out that they are an ancient immortal race that protects the planet. They were all hibernating because they had caused an ice age to envelope the world thousands of years ago. They did this because humans were recklessly destroying the planet. One of the group is actually a decendent of the 'sentinel' that they left awake to awaken them when the ice age was over (hence why he could wake them up).
Now that they have woken up to find that humans are once again ravaging the planet, they decide to make the planet go into another ice age. The decendent of the sentinel, believing that humanity is not beyond redemption, finds out how they hibernate, and makes them all fall back to sleep.