The prostate gland is an internal structure, behind the base of the penis and just beneath the bladder, which wraps around the duct that leads to the urethra. It produces a portion of the fluid that semen is made out of, and can often be felt about two inches inside the anus if you press your finger towards the base of the penis. Many men find pressure against the prostate gland (which by its nature also slightly stimulates the base of the penis) to feel pleasurable or at least interesting, particular when they are very aroused or close to orgasm.