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Looking straight down into the crew hatch, wiring bundles snake across both the floor and the platform on which the mission control programmer rests.

Also note the latch keepers on the sill, which were used for the spacecraft's Block I hatch.

Although it flew after the Apollo 1 fire, the unified (Block II) hatch was not yet ready for the flight of Apollo 4 (Apollo 6 would be the first spacecraft to fly the new hatch). However, Apollo 4 flew with a test panel in place of its hatch window which was used to help qualify the redesigned hatch.

The Block II hatch was called a "unified" hatch because it was a single hatch; the Block I hatch had inner and outer hatches, which had to be removed separately. The Smithsonian has a page with Apollo 4's inner crew hatch. There is a line of latches along the bottom of the hatch which engage on those on the hatch's sill.