I have a nice, cut-away diagram showing the interior of of the Saturn V S-IC first stage, including the interior of its liquid oxygen (LOX) tank, but sometimes photos are more informative than diagrams.

While I have seen these both of these photos online for many years, I don't think I've ever found a definitive source for either of them. I found these photos simply by running a Google Images search for "S-IC LOX tank interior."

This first photo is a view from the forward end of the LOX tank looking aft (presumably taken from the hatch on the tank's forward bulkhead).

The openings for the five LOX suction tunnels are visible on the far tank bulkhead; the center one appears to have its anti-vortex device installed, while the four outer ones appear lack theirs. Also note the cruciform baffle, installed at the bottom of the tank to further guard against vortexing.

The technicians are working in the general area of the helium bottles (#23 in the above-linked Major Components diagram), although they appear to be working on a different component which I am unable to identify (my guess would be a level-sensing probe, of which the S-IC LOX tank has four, although I do not see such probes listed on any reference diagram at my disposal). The helium bottles held high-pressure gaseous helium which was routed to the F-1 engines' heat exchangers where it was expanded and routed to the S-IC's RP-1 tank to provide ullage pressure (#24 in the above-linked Major Components diagram).

The anti-slosh baffles on the tank's walls are about mid-thigh high on the technicians.

I speculate that the two darker-colored plank-like objects laid atop the anti-slosh baffles near bottom center are walk-ways or work platforms; there appear to be two floodlights on the left-hand plank.

Click image for a 1800x1432 pixel version of this image in a new window.
From the Internet at large (I was unable to identify an authoritative source; if you are aware of the photo's origin, drop me an email).

The view below was taken from the aft looking forward.

At center of the forward tank bulkhead is the access hatch. There are several other white, circular spots on the bulkhead. One would be for the LOX vent, and there's another opening for some sort of tank access which I have been unable to identify. I'm at a loss for what the other spots are.

As with the photo above, the walls have anti-slosh baffles mounted on them, and the helium bottles are located toward the bottom of the photo.

The anti-vortex cruciform baffle appears around the edges of this photo; the circular bracket at center is likely to support the center LOX suction line. The center LOX suction line extended into the bottom of the LOX tank, as inboard engine cut-off was approximately 25 second prior to outboard engine cut-off.

Click image for a 1077x1337 pixel version of this image in a new window.
From the Internet at large (I was unable to identify an authoritative source; if you are aware of the photo's origin, drop me an email).