The Paired Locket:
This is a large, brass, heart-shaped locket with two harsh scratch marks over the surface. The locket is matched with an exact identical. When you open the locket it creates a small portal to the other. This is how two lovers would be able to communicate with each other when they were apart.
If your adventurers find both lockets, they will be irreplaceable communication devices. Most likely your adventurers will find one, but what’s on the other end? An ocean, a strange but exciting character, or even better, space? They’d get a jet of water, a plot hook, and a vacuum. Awesome possibilities and fun play!