@Sandy, I'm not sure I agree with using levels as a motivation to explore new areas. I see levels as a tool to challenge and to give chances to grow by gradually increasing difficulty. For me levels have to be connected. You learn new skills/trick that you can than use later on in the game. So I absolutely agree that there is motivation in levels to grow and to challenge yourself, but i don't think it's the ('right') motivation to explore.
Exploring for me is about curiosity for the yet unknown, the half known, the what if I... It's about making choices: do I continue on this road and see where it leads, or do I go left? Or right? For me the possibility of choice is necessary for exploration: the choice to try different things, work with different materials, ... So to make choice possible, options should be visible, (what doesn't mean that it should be clear what the options are exactly.)
I'll try to work out a framework for the game tonight, that might make it clearer.