I am back! 😀
With fresh relaxed mind I can resume work on my project.
During our trip to Wales one day we went to Anglesey. I spotted some king of growth on the stones on the beach. Shell kind shape some of them with opening in the middle.
I thought I would use a shape of the growth and a mechanism of that plant and create some kind of growth on the underground walls which react to movement. Open and close when someone pass by.