Here's a nice little challenge for you to try this weekend. For those of you with Halo: Combat Evolved Anniversary, and are looking to make an easy 25G, this is for you. The 'How Pedestrian' achievement asks you to walk the entirety of the level "Halo". You know, the massive second level of the game. However, there's one big obstacle standing in your way, and that's where the Achievement Hunters come in. See, you have to grenade jump your way across a pretty large gap. I'd try to explain it, but I'd probably mess it up.
I remember being in awe at how massive the level was when you were travelling by Warthog. But I can't imagine traversing the gargantuan level by foot.