I semi-tried to get this out before going on vacation, but it didn't happen.
In this chapter Ashinano is presumably riffing on the "Umihotaru" island that sits in the middle of the Tokyo Bay Aqua-Line, a $10-billion-dollar public works project that consists of a bridge and tunnel connecting Kawasaki, on the western side of the bay, to Kisarazu, on the eastern side.
View Larger Map
Given the way this chapter goes, for a while I thought I had screwed up some dialogue in chapter 10, but now I think it makes sense... I'll have to double-check.