As soon as you exit the tunnel, stop and notice that there is a side path to the left (it goes upwards). Drive up there...

... and halfway through the path look for a vase. Dismount and break it to get the Treasure (16/50).

Continue down the patch, but do not exit to the main road yet. To the part where the path goes down and meets the road, look for another vase hidden in the bushes ahead. Break it and collect the Treasure (17/50).