The above pictures shows a Lego Duplo railroad that Olli and I built in summer 2005 for my youngest son Janne. This railroad consists of 10 bridge elements, runs at 11 different levels and reaches the height of 1.4 meters at the top. It takes about two minutes for the Duplo train to reach the top from the floor level, and slightly less to get back. (Interestingly, the autosleep feature of the train is not designed for this long railroads; once it gets to the top it shuts itself off and you have to start it again to make it continue the journey.)
This model consists of about 2500 Duplo bricks and took about a day to build. You need roughly the following Lego products in order to build a similar model:
Motto: If you build from Duplo instead of the regular legos, you get bigger models.
Additional pictures below: