I love exploring the physical environments that I find myself in, in dreams. Houses with rooms that go on forever, cluttered with interesting, rich objects - bolts of cloth, or boxes with opening mechanisms and things inside. Or sometimes landscapes where I can't get over the 'realism' of the grass, the hillsides, how real it all seems - whenever I become lucid, that's mostly what I focus on. Touching, exploring the physical things and being amazed by how real they look and feel. Like some others posting their replies it's the sense of control which is good, though I do have trouble giving myself permission to be in complete control and exercise the freedom which lucid dreaming gives.