Loz Architecture Tokyo Sky Tree
Over 620 pieces, level 3 difficulty.
The Sky Tree comes in at around 40cm tall when built and is actually a very tricky build - having built thousands of nano models I would quite happily put this as a 5 star difficulty rating, so don't be fooled.
My pro-tip on this one would be to look very carefully at brick placement as you work your way up the tower, as if you don't, you'll find attaching the top section difficult. It also helps to remove the product from the base section while building the lower/mid layers as you'll be able to press everything together much firmer.
Do not attempt this model unless you are an accomplished nano-modeller - it's pretty fiendish and you need to have your hand weighting just right to avoid dislocating previous layers. If you can manage it though, it's a satisfying build which looks great!