Jewel World is a Thomas the Tank Engine film, that was featured in theaters. It is the most successful Thomas Film of all time, pulling in over $100,000,000 from it's $19,000,000 budget.
Jewel World was released on January 13, 1993, and received positive reviews. The film was nominated for two Saturn Awards (one for Voice Acting, the other for Camera Shots).
Thomas the Tank Engine is puffing along his branch line, when he is suddenly picking up speed. He crashes into a pair of buffers, and notices he made a whole into a large rock. The hole is big enough for someone to walk into, so his Drivers check inside to see what's inside. Once they're inside, they found lots of Jewels.