Tunnel leading from fore pressurized section to aft section.

The fore, aft, and tail gunner sections along with the tunnel were all pressurized. The two bomb bays were not pressurized.

Note: part of the round access hole leading to the fore bomb bay can be seen directly underneath the tunnel and at the bottom of the photo.

Typical B-29 war-time crew was 11 men:

The pilot, copilot, bombardier, flight engineer, navigator, and radio operator were housed in the fore pressurized section.

The radar operator along with the top gunner, port waist gunner, and starboard gunner were housed in the aft pressurized section.

The tail gunner was in a separate pressurized tail section.