Inktober the 28th for the late Iain M. Banks.

What brings you to "The Last Party", located on the Equatorial 353, a giant derigible navigating the circumference of the planet inside the hollow tube struts of a worldwide bit of incomprehensible architecture and art left behind by a race long since sublimed into pure energy? Only a small hitch before our civilization ends as we know it.
And don't ask me why the main character has four arms. Read a book why don't you.

The Hydrogen Sonata by Iain M. Banks.