To see all the blocks and landmarks you've collected, go to the Menu page and select the Collections tab. There you'll be able to see notebooks of all your completed tasks divided by theme. Inside each of these you'll be able to view the blocks and landmarks you've collected for each theme, as well as the number of days you've used the theme. You can also head to the Shop tab and look under "My Themes" to see which themes you've collected so far.