What substance absorbs the most moisture in a given time

Condensation happens whenever hot air meets cold surfaces, and the air after a shower is hot and very humid.

You'll always get some condensation, but there are a few things done to mitigate this:

• Normal interior walls and well-insulated exterior walls are usually not a lot colder than the air temperature. (The colder the walls are, the more condensation will happen.)
• An exhaust fan will remove some of the humid, hot air (and since hot air rises, the exhaust fan is on or near the ceiling which has the greatest effect), and regular (room temperature, and regular humidity) air will be drawn in from HVAC vents or under the bottom of the door. Opening the door will help even more.
• A semi-gloss or high-gloss paint is used (usually these are labelled Kitchen and Bath) which holds up better to high humidity, condensation and regular cleaning.

If your walls are actually solid concrete or concrete blocks, then they definitely are going to be colder as concrete is a poor insulator. This is why in the same room concrete will feel cooler to the touch than drywall, which will feel cooler to the touch than a towel.

Multi-part answer here:

1. It could be the water table, in which case, there's not a lot you can do. If it's the water table, then you'll have water seeping up through the floor. BUT consider that when they built the house, they dug a bowl in the ground, and then backfilled with loose soil, rocks and whatever other garbage they had lying around. You could have a permeable (gravel and sand) fill inside a relatively impermeable bowl (clay). In this case, sloping the ground away can help. It will at least get rid of standing water up against the foundation and help mitigate anything flowing through the walls.

2. The major worry is mold. Make sure the area is clean, so that there's nothing for mold to feed on. You can spray with a biocide if you see any growing, and certainly don't enclose it by adding drywall over the area.

3. If you have rising damp, then an internal sealant won't do anything. the hydrostatic pressure will force water through. A dehumidifier will remove the symptoms.