I happen to have some castor oil, but couldn’t remember why I bought it.  So here is a long article on medicinal uses:
CASTOR OIL – Natural Protection from Deadly Viruses

… Oftentimes there is no need for castor oil packs; amazing results can be obtained by simply applying it directly to the skin. The following is a short list of some of the more common ailments it can remedy:
skin keratosis
fungal and bacterial infections
abdominal stretch marks (prevention)
sebaceous cysts
senile lentigo (“liver” or “aging” spots)
muscle strains
ligament sprains

There’s also an excellent description of the lymphatic system and the benefits of castor oil:

Others have found it useful in eliminating chronic problems with epilepsy, hyperactivity, liver and gallbladder diseases and chronic fluid retention. (Fortunately, to benefit from this and other natural therapies you really don’t have to understand how they work.)
McGarey has reported that, when used properly, castor oil packs improve the function of the thymus gland and other areas of the immune system. More specifically, he found in two separate studies that patients using abdominal castor oil packs had significant increases in the production of lymphocytes compared to increases among those using placebo packs.
Lymphatic Congestion
Obviously, conditions known to be related to poor drainage of the lymphatic system will tend to benefit from this type of therapy. These would include complaints such as:
1. chronic fluid retention with swollen joints and pain
2. arthritis
3. upper respiratory infections involving the sinuses,
tonsils and inner ear
4. colon problems like Crohn’s disease or colitis
5. gallbladder disease
6. boils
7. liver cirrhosis, hepatitis, enlargement or congestion
8. menstrual-related congestion
9. appendicitis
10. hyperactivity
11. constipation, bowel impaction or adhesions
12. swollen lymph nodes
13. bladder and vaginal infections

The article is definitely worth reading in its entirety.