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 Europe

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

just complete all the challanges in europe online...except for the 2 that you have to do online the others can be done solo...and make sure that u are actually online, if you change mountains you have to go online again

Just play every challenge online in europe. 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.