Costume Quest

I just won this Achievement about ten minutes ago, and ALL 15 RAMPS CAN BE FOUND ON THE VERY FIRST LEVEL (Auburn Pines Suburb) while trick-or-treating.

The level is divided into two halves: before and after you help the school principal, Ms. Putterpam (near the park), who won't let you enter the second half of the level until you get the ingredients for her pies to save gym class.

The first 10 ramps can be located in the first half of the level. Some of them are tricky to find, so count them down as you come across them. But there are 10 of them there, and you should not proceed to the second half of the level until you have found them all, to make this Achievement easier to get.

And the final 5 ramps are located in the second half of the level, and are all really easy to locate, as once you locate one, the rest follow in quick succession.

Totaling all 15 ramps, and the Achievement.

Based on when I got this achievement, here is what I can assume:

There are 13 or 14 ramps in the first area, where you get the Robot outfit. You must jump a few of them for quest-related items, but many are completely optional. Make sure you travel down every road and look for a ramp to take you into a park, or behind the Trick or Treat homes.

This usually leads to a number of additional ramps, some times branching in two directions, so make sure to double back and take the other direction to cover every ramp. If it is your first playthrough, you should be hitting the X button on everything in sight to get candy. If you've been through the area if nothing is telling you to hit it, and there is no candy on the ground, use that to tell if you've already been through that area.

In the 3rd area, with the Carnival, I jumped off one of the red ramps that look like barn doors. I don't know if that actually counted, which is why I'm not sure if there are 13 or 14 ramps in the first area. Once you enter the corn maze and complete the last costume, you will enter one last area after fighting a guard.

Continue left, and you will reach a hard-to-see ramp. The ramp looks like a shadow, so be careful not to miss it. As I recall, the last ramp was facing left into a narrow vertical alley of the maze with a line of candy running up it. I spent most of the game with Reynold in the Robot costume to get around faster, so I hopped up and over the ramp before I realized it. The achievement unlocked as I landed.