Long ago, I watched an animated TV show or movie probably on Cartoon Network India. Here are details I can recall:
There was an Island in the ocean which was surrounded by big canyons. And, water from ocean was of course flowing down in the canyon like Asgardian water fall without an apparent bottom.
Our heroes were on a boat which was dragged by the water flow, but due to Kinetic Energy, they luckily didn't go down. They landed on the island. In order to escape, they tried bridge making blah blah, but without any luck.
On island, they learned that there was already a guy there trapped for very long time turning old. He crashed on the island with his aeroplane which was in no condition to fly again.
On island, there was an inactive volcano (with sideway opening, not top). That trapped old guy spent decades to carve the mountain outside to make it look like a dragon, in a hope that one day volcano would erupt and it would look like a dragon breathing fire.
In the end, they escaped from the mouth of the dragon using steam power when volcano erupted. Exact setup isn't in my mind, but they escaped on a boat which safely landed on water outside.
In the very end, when the old guy turned his head around, he saw dragon breathing fire and became happy admiring his work. And then, the island sunk down in the ocean probably due to volcanic activity.