I am first year graduate student and following the Thurston's book on 3-dimensional geometry and topology. Among all the 8 geometries of 3-manifold (from Thruston's classification), I heard from some of my colleagues that the Geometry of the Heisenberg group i.e. "Nil-Geometry" is actually a very rich area in last 10-15 years. I am really excited to explore on Nil geometry but didn't find much sources on internet. Can anyone suggest me where should I start? and

Thanking you all in advance!!