You encounter Surok three times in short cutscenes in the tunnels, based on the route you take:
In the first encounter, in the deadly red spider room, you see him kill two fire giants in one hit (6700 life points each).
In the second encounter, in the skeleton's room, you attempt to stop Surok, but he summons two big wolves—not to mention the undead already in the dungeon—to attack you. Do as you wish with them, but you can simply run past them to the next portal.
The last encounter is near the Dagannoth room (which is in the most north-west region of the Chaos Tunnels). In the Dagannoth chamber, look to the west for a portal with the familiar footsteps. Enter it, and you find Surok for the final combat. Using Protect from Ranged is recommended.
Enter the last portal in the Dagannoth chamber to find Bork. You see a cutscene, where Surok summons Bork (level 107), who fights exclusively with melee. He has fairly high defence, but is weak to crush attacks. He is immune to stuns as well as poison and deflect damage, and his melee attacks can hit well into the 2000s.
After you have discovered Bork, you can leave and restart the fight again. You can use any of the quicker routes mentioned on Bork#Getting there to get to reach Bork without travelling through the whole of the Chaos Tunnels.
Turn on Protect from Melee or Soul Split, and attack him. Ranged is not recommended as he is extremely resistant to ranged attacks. Magic works well, though.
When Bork is at 3/4 health, he will summon two to four Ork legions (level 70) to attack you. If you stand near them, they will attack you with melee. Otherwise, they will attack you with Ranged.
Surok attacks you every 20 or so seconds during the battle, with magic that can hit into the 500s-600s. He cannot be attacked, however, as a magical force will stop you from doing so.
When you defeat Bork, he falls to the ground. Surok, realising that he is defeated again, then calls Zamorak for help and teleports out of the cave.
Quickly, grab the monster's drops and get out, for the cave will be collapsing. You will lose some life points if you stay in the cave too long.
Borked is Internet-technical slang for something that is broken, as in "that update borked" or "you totally borked the time rotor." In this case, the portals in the Chaos Tunnels are borked. This derives from political slang, originating with a judge who was nominated for the US Supreme Court in 1987, Robert Bork. The opposition party rejected his nomination, in what was a rare occurrence up to that point. Consequently, his name became a synonym for when any nominee for a political post was not confirmed. The 2002 Oxford English dictionary defines bork as US political slang meaning "To defame or vilify (a person) systematically, esp. in the mass media, usually with the aim of preventing his or her appointment to public office; to obstruct or thwart (a person) in this way."
Bork is reference to the Borg, a race in the Star Trek universe who seek to forcefully add other species into their collective. The Ork Legions that Bork summons may shout phrases such as "We are the collective!" and "Resistance is futile!" which are references to the Borg in Star Trek.
Bork is also a portmanteau of the two words Big and Ork. This is played on in his examine text, which says "That's one Big ork."
"The Hunt for Surok" is a pun on the Star Trek movie The Search for Spock. Surok is also similar to the name of Surak, who was the Vulcan who instituted the philosophy of logic over emotion, which caused the split of the Romulans from Vulcan.
Interestingly, Members who have completed What Lies Below can start the miniquest on free-to-play servers. They can encounter Surok near the entrance, and see the cutscene where he enters the tunnels. However, they cannot enter the tunnel itself, thereby preventing the miniquest from progressing further.
The RuneScape news article about this miniquest contained the line "for there are worse things than simple orks in the dark places of this world." This is from The Lord of the Rings: The Fellowship of the Ring when the characters go into the Mines of Moria.