Cross the bridge and go up to the high road. At the cracked wall, use grapple on the plug, build a structure. Jump onto a bomb, place it in the device and useHammerto detonate it.
Now, go up where the wall was blown off (Minifig 1) and climb up. Up there you should be able to slide down and pick up the scroll, if you haven't already in the story walkthrough.
Don't do the race yet. Close to the pool in the road, jump onto the bridge rail and look down. Jump onto the rope that goes across the river and get the Brick on the other side. Then return to the high road.
The race ends at the river side below the high road. There's a closed area in front of you. Open it with enough Gold Bricks, go inside and use Scanning to open the gate.