Hang 10-Squared

You slide when a slope is too steep to walk down, so all this needs is a long, smooth descent. Find a decent mountainside, or carve your own with the terrain tool - a steady spiral ramp down a big hill works a treat - and keep pointing downhill for a clean 10 seconds.

If you're building it, make it steep but smooth: bumps and flat spots interrupt the slide and reset the clock. Digging a long angled tunnel underground works just as well and is easier to keep consistent.