Castle Quest Set (also known as Quest for the Crown Set) is a TrackMaster set by Fisher-Price in the King of the Railway series. The set has several interactive features, most of which are activated by protrusions on the included red truck. These include a collapsing bridge; a crane that places sections of track into gaps when the truck flips a switch (alternatively, this can be replaced with a normal curved track to accomodate longer trains; and a gate that closes once a train passes through it. The set's main gimmick is the mine shaft. The track above the shaft leads to a dead end, but once a train goes over it, the track caves in. The train then comes out of the mine and, if the truck is part of the train, the crown will now be in the truck.
Thomas with interactive Red Truck with Crown cargo piece