Shaun White Snowboarding

The other solution from SuperTim1337 is right but I think it makes it seem like a quick and easy cheevo and after trying for it, I found that there's more to it.

You are going to need to play through the single player mode in order to get this achievement because one challenge in each area is locked until you complete Shaun's challenges of collecting coins etc.

I also think that you don't just need to play every challenge but you have to gain at least one medal in each challenge.

These are the challenges you need to complete in Park City

** NOT IN ANY PARTICULAR ORDER **
--------- Can be done solo as described in other solution
1. Slopestyle 1
2. Jibfest
3. Big Air
4. Collect
5. Precision Riding
6. Death Race
7 & 8. Ground Tricking 1 & 2
9. Air Time
10 & 11. Air Tricking 1 & 2
12, 13 & 14. Freestyle 1, 2 & 3
15. Halfpipe (Unlock this via Shaun's challenges, single player)
---------------- Must be Multiplayer -------------------
16. Rat Race
17. King of the Hill

Just play every challenge online in park city. You can do this by yourself by hosting a session and then go to the challenges and press the y button instead of A to invite people. On the 2 multiplayer challenges you have to play with others, though.