The scrotum holds the testicles. This is a very sensitive and a very delicate part of any man's body but remains a highly erotic area. Applying too much pressure to the testicles will cause pain. Just keep in mind to go very gently.
Play with the testicles gently with your hands. You can also suck or lick the scrotum and if you put them into your mouth (with the minimum of pressure) you will see your partner lost in the moment.
All the body creases are very sensitive (the inside of the wrists, elbows, back of the knees). The crease between the cheeks of his buttocks and the bottom of the bum is very sensitive to stimulation.
Learn about the erogenous zones on a woman here.