What are good DUPLO projects for around 2 year olds? It is always good to have a bunch of (short) building projects to suggest to our toddlers.  Here I would like to collect some easy ones for DUPLO.

I'm not particularly interesting in creating duplicates of real world objects, like building animals, houses, etc.  The projects can be abstract, focus on something unexpected, or whatever.

Please share your experiences.
And here is my first project: Color towers:

Building towers is probably the first directed building effort that toddlers undertake.  In this project I gave our son (20m) many bricks and built 4x4 monochromatic socles for towers.  I told him that we are building a 'green', 'red', and so on tower.  At first he only got that we are building towers, but I directed him toward using only the color that is already in the socle and after two or three wrongly placed colors he got it.  After a few layers he even asked for specific colors to continue a specific tower.  After the towers were high enough, together we inserted some nooks for figures to stand in.  He did most of the building, and I only occasionally changed the orientation of some 2x4 bricks to make the towers more stable by interlocking.  The visual impression of the result surprised me: