The Glute-Ham Raise is one of my favorite exercises.
What is it? The glute-ham raise is an exercise for the hamstrings and calves and gluteals, done either with a specialized apparatus (sometimes called a glute-ham bench or a GHR) or on the floor with a partner. You lower down until your legs are straight, and then contract your hamstrings hard to pull yourself back up to vertical. Your calves push hard against the footplate of the apparatus in order to finish the movement, taking you past vertical to a "leaning back" posture. Repeat.
Although EXRX says this is an isolation exercise (motion around one joint), done on a glute-ham apparatus, both the knee joint and ankle joint will move to complete the movement.
If done with a partner, this is often called a "natural" glute-ham raise. The partner holds your ankles, and you use your hands to brake your fall during the eccentric portion and provide a small boost during the concentric portion. Here is a good video of "natural" glute-ham raises:
EliteFTS sells a number of excellent glute-ham benches, and also produced this extremely complete article on variations and techniques.
16 Ways to Maximize your Glute Ham Raise written by Dave Tate.
A number of DIY glute-ham raises have been featured on YouTube videos, as well, such as this one from Ball State, using a pulldown bench. It's also possible to simply use a knee pad and a heavily loaded barbell in a power rack.
Ironically, in this excellent video by Martin Rooney, he says no one ever lists it as a favorite:
For me, it is. It's not technically hard to do - you don't need to learn technique, just how far to go down and up. Then it's just hard work. It perhaps doesn't hurt that the first time I did them, it was a "natural" (floor-based) glute-ham raise with a partner, and I could barely do one without just falling face-down on the mat. I knew I needed to get stronger. Now, sets of 10 on the GHR at bodyweight are warmup, and I need to add resistance.
Why should I do these? They are an excellent exercise for your hamstrings in specific and your posterior chain (back, gluteals, and hamstrings) in general. They are not technically difficult to do, but brutally hard when appropriately weighted. The strength you gain doing GHRs will transfer quite nicely to other exercises that demand strong legs, and to sports as well. Give them a try. I won't lie to you, they'll be hard (or you can make them so), but they are worth the effort. Glute-ham raises will reward you for the effort you put in many times over.