Titian?
I have read that Titan may have liquid water under its icy crust.
I find this a fascinating concept. A world with two surfaces and two environments. One surface is rocky and covered in an ocean of water. The other is an ice surface covered with a nitrogen atmosphere and pockets of liquid methane. Perhaps the lower world invades the upper world in the form of ice volcanoes.
What would be even more fascinating if the lower world had water based life and the upper world methane based life.