Book du jour - more tunnels

When the chain of 1" squares didn't fit easily into the 1" holes, I tried making a chain with 3/4" squares - but they were too small -With a little urging, the 1" squares squeezed in -
and now sit there quite happily -
Here's one I made some weeks ago, from plain white paper, with a few squares previously cut from black paper added in -
There could be scope for using the colours (and stations) of each tube line -