I don’t know whether it counts as weird, but there were lots of more or less complete plans to build a Channel tunnel and even some digging (
https://en.wikipedia.org/wiki/Channel_Tunnel#Earlier_proposa.... Funny quotes:
“concerns about hordes of tourists who would disrupt English life”,
“a Royal Navy officer in the Directorate of Miscellaneous Weapons Development calculated that Hitler could use slave labour to build two Channel tunnels in 18 months. The estimate caused rumours that Germany had already begun digging.”)