Many professional athletes jump into ice-filled bathtubs after a strenuous workout. Some of the rationales behind putting your body through such extremes is very much straight forward. The low temperatures instantly cool the muscles down; which is an efficient way to bring down inflammation.
Muscles that are overworked become sore due to a chemical called lactic acid. When your muscles are put under heavy stress they begin to get deprived of oxygen and lactic acid starts to build up causing the inflammation.
Ice baths help the blood vessels and the muscles to momentarily constrict which helps get rid of all the waste and byproducts from a strenuous workout. Once the body begins to warm up from the ice bath, the muscle tissue that was affected begins to increase in blood flow. That increase in blood flow helps with the muscle recovery.
If you have never done this before, it is obvious that it will suck and will be very unpleasant. Just remember that that unpleasantness is temporary.