An ordeal is a painful or trying experience, test, or challenge.
Pleasure in the ordeal
In BDSM, for some bottoms, and in consensual spanking, for some spankees, the ordeal is what they enjoy about getting whipped or spanked. The "ordeal-seeker" is a type of bottom. They like to remain stoic during the punishment and their reward is the feeling of pride and strength that comes from enduring suffering — in a similar way that people climb mountains, run marathons, or eat hot chili peppers. The dolorous element of these activities makes part of their appeal.
Endorphins can explain for some of the high feelings that come with activities involving physical challenges and pain, but the ordeal-seekers find reward in the suffering itself — in the awareness that they are voluntarily going through this and are strong enough to endure it.
Like many spankees, ordeal-seekers often wear their marks with pride, as visible proof, lasting for days, of what a hard spanking they went through.