Remote Control Cars

Partly fill a number of 2 litre drinks bottles with something that will weigh them down. Don't over fill them as they need to topple when knocked. Alternatively something like cardboard toilet rolls tubes could be used.

Next arrange the bottles over an area that is suitable for a remote control car (grass and thick carpets are not good unless you have a particularly good remote control car).

The treasure hunters must negotiate from one side of the room to the other without knocking down the bottles to win their next clue.

A good addition
This only works if you have a large patio or similar, which is overlooked om a 1st floor window.
Fill the bottles as above, but fill them with water so that when toppled the water spills out. Next, draw the location of the next clue onto the patio using chalk. You could draw arrows, a map or words. Make it complicated though - from ground level it should be less easy to make out what it says. From a 1st floor window it should be clearer.
The treasure hunters stand near the patio and try to get their car from one side to the other. Every time they knock over a bottle the water washes away some of the clue. Only once they get their car to the end are they allowed to go upstairs to look out the window at what's left of the clue.
Don't worry about the entire clue washing out - it is unlikely that it will. In fact, even the bits where water has washed over it may still be visible, but the fear of it rubbing out will be there as the hunters attempt to complete it.