Lake Of The Long Sun: Gene Wolfe

Patera Silk is a dedicated young auger whose parish buildings are about to be sold for taxes. He has made a pact with the wealthy, sinister Blood to get the money to save them. And so Silk has embarked on a quest which reveals to him the hidden secrets of his world, a huge starship illuminated and warmed by the artificial Long Sun, a spaceship so vast that remote cities can be seen in its sky. Silk travels to Lake Limna and visits a shrine which conceals an entrance to the sub surface passages of the ship, to rooms that contain strange machinery and stranger beings - and to rooms with windows...