This is simply amazing. Titled Project Indigo, it's a concept by artist Jesse van Dijk. In his own words:
Project Indigo (working title): Design of a vertical seaside metropolis
In december 2007 I sketched around a single theme for a while as a personal side project. I tried to envision what a huge -vertical- seaside city would look like in a world were dry land is very precious. This city would be situated on a huge pillar in a 'cavity' in the sea; possibly an inactive volcano crater of some sorts. I assumed a level of technology of western European countries around the seventeenth century. Naturally I had to take some huge liberties with the actual mechanical possibilities of these constraints to make a city in a hole in the sea work, not to mention a vertical city.
As far as technique was concerned, I was not interested in creating pretty pictures, but I wanted to present a more or less solid approach to the theme described above.
I'm completely enthralled by this work, particularly the last four images. My imagination immediately begins burrowing and building...