This is level 64 of the Main Tunnel.
Always be ready to long jump as the Runner. This level is a test of reactions and judgement. Don't sink too low on the crumbling tiles, but don't jump the second you make contact with the crumbling tiles. as you may undershoot. Alternately, you could use the Bunny, allowing you to make progress very, very fast indeed.
That should get you to Level 65, the last level of the Main Tunnel! Woo-hoo! Hang in there. Nearly at the end of the Main Tunnel! But this is the penultimate level. The next one's hard.