Skyrim Sidelines- Bloodlet Throne: The Consequence of Poor Planning...
Once the wolves are dead, you're likely to find yourself facing the animated dead mercenary and bandit who were the wolves' previous opponents (oh terror) before you get a chance at the pull-chain to open the third spear-gate. Sometimes, however, the vampires won’t even animate the corpses until you’ve released yourself from the makeshift arena and come up on to the observation platform to face them on even ground. Why the pull-chain to admit you to Vighar's platform is in the pit with you is anybody's guess, but there it is and you can use it to head up and murder the moron.
Vighar is, of course, a vampire lord, which makes him remarkably powerful- but he is thankfully not very versatile. Mostly he will drain your health with his vampiric spell, intending to heal too quickly for you to kill him before he drains you dry. How much of an issue this is for you really depends on your level, both overall and in terms of your relevant weapon or magic skill. By the time you're around level 30 it should be relatively easy (though slow) to succeed here, and an increased level only makes it faster. Do be aware that the spell always has a chance of afflicting you with Sanguis, the vampire-creating disease. Fortunately, Cure Disease potions are easily found and, if that doesn’t suit your tastes, you can simply pray to the Aedra at one of the many shrines of the Nine Divines- even if it isn’t in a temple, the blessing will still clear you of all diseases, thus restoring you to natural health so long as you haven’t given the Sanguis a chance to finish taking hold and fully turn you to vampirism.
With Vighar dead, head into the tunnel behind his platform and dig up some silver ore. Continue along the passageway to retrieve the contents of a highly valuable chest, and then you can proceed to the backside of that barred door you found in the first true room. This is because you have finished- the Bloodlet Throne now sits empty, the vampires here all slain. Unbar the door and walk out triumphant- and, if you were sent here by another, go receive your reward for a bit of work well done.