As OP posted in a comment, this is Nightlord: Sunset (2006) by Garon Whited, the first book of the Nightlord quadrilogy. An audiobook has indeed been released.
A guy gets turned into a vampire after hooking with a girl. He doesn't realize he is a vampire and goes home.
From Goodreads summary:
Eric didn't ask to be a vampire. In fact, he didn't even believe in them. Then he hooks up with a hot babe, wakes up with a hangover, and bites his tongue with his own fangs. Which pretty much settles the question.
Now he's trying to hold down his day job while learning the rules of the Undead -- the most important being that bloodthirsty urges and predatory instincts are a real bitch.
Upside; Eric has the beautiful Sasha to teach him the ropes, including the magic he'll need to survive.
After the girl gets killed by followers of the sun god (I think that is right) he creates a portal to the world they come from. Then goes there to kill them for killing the love of his life.
Downside; they're being hunted by members of the Church of Light, who are determined to rid the world of vampires.
Then Sasha is killed, and Eric is thrust into an alternate world in his quest to avenge her death. There he becomes a Nightlord, fights a dragon with the help of his magical steed, Bronze, and upchucks a sword named Firebrand.
As for the other info...
I also remember he can walk in the sun
This review mentions Eric being a "Day Walker".
She changes him into what they call a day walker. A type of vampire that can come out during the day and during the night.
I remember there is a circular concrete pond that he uses as a portal, and has to kill a herd of cows to power it
Might have been a single cow, per this review:
I didn't like the part where Eric had to sacrifice a cow in order to successfully complete casting of a magical spell intended to show them the location of their organised enemies called The fist of God who tried multiple times to kill them.
The "magical spell supposed to show a location" sounds like a portal of sorts.
I think in a later book in this series he creates a mountain fortress that is kind of alive. In his smithy area the mountain produces metals for him.
Eric becomes "Halar the Undying" in the later books, and infuses Mount Karvalen with his vitality. From its wiki entry: (the Wiki is part of a Nightlord site which is apparently supervised by the author, so it seems a reliable enough source)
According to Karvalen legend, during the exodus of Halar the Undying, when he gathered together those who would follow him to found Karvalen and Mochara, he filled the mountain with some of his own vitality, bringing it to life.
In a matter of days, the spirit of the mountain moved through the bricks and stones, engulfing the whole of the walls, and merging the disparate components–brick, stone, mortar–into a single, giant slab. Since then, the wall of Mochara has grown slightly taller, considerably thicker, and remarkably uniform and smooth. The mountain has done something similar with the city streets, turning mud to rock, smoothing it all over, and even developing underground tunnels for rain runoff and the like.
If the mountain can do stuff like that, I reckon it could produce metal.
Also his tentacles are hard like steel cables but later on he meets other vampires that have feathery tentacles that can brush across people and drain them of a small amount of their power.
Eric/Halar is part of the Nightlords vampires. According to this review, the Nightlords have such "strands"; it is possible that what drains life force also drains power.
Nightlords feed off of humans needing their blood and there life force using invisible strands of darkness.