Before-and-after photos show how a man turned a crumbling 'dungeon' into a stunning $590,000 apartment

The Georgian-style building was originally designed by Thomas Warr Attwood, a British architect, in 1768. Though Barrow's apartment is two floors, the building was originally just one home.

"These buildings used to be big townhouses, and the whole building would be a private residence. Since then, these have all been turned into apartments," Barrow told Insider.

He discovered the apartment while renovating another home in Bath.

"Basically it was just left to rot away because they didn't do anything with it," Barrow said. "No one would spend the money needed to bring it up."

He added that it was in such bad condition that it was deemed a fire risk.

"I approached the people who owned the building and asked if they'd be interested in selling it to me so I could restore it," he said.

He said that after much persuading, the owners agreed to let him purchase and renovate the property.

"It restricts you on what you can do to a property. Grade 1 is basically the highest you can get. They're saying that everything, outside and inside, has historical significance, and really limits what you can do. You can't build walls, you can't take walls out, even if something is falling down, you have to repair it rather than replace it," he said.

But Barrow and his friend, who is an architect, were able to work together to put together a plan that they believed would be accepted by the listed building offices.

"It wasn't actually a dungeon, but it was a very scary place to come down to. When you came down before, the doors were falling off, there was no light, it was like something out of a scary film like 'Saw,'" he said.

"I was able to prove them wrong," he said.

"Every single detail, to even cross sections of the door, what the wood is made of and the shape of each little panel on the door" had to be accounted for, according to Barrow.

Though the actual renovation process only took about five months, Barrow said that a lot of time was spent negotiating and discussing details with the other leaseholders in the building.

"Our assumption is that it had never been lived in since it was a terraced house back in the day, when they didn't have any of those services," he said.

"We assumed that these areas are where the kitchen and wash areas were, and where they stored coal and food," Barrow said.

"At some point in its past they ripped up the Bath stone floor and put in a floor that did not go with the rest of the property," he said. "On the upper level there was original Bath stone flooring, so we assumed that at some point, on the lower level, there was Bath stone floor."

But getting new stone wasn't as simple as going out to buy it.

"They don't do that, so in order for us to get Bath stone we went to the mine itself, where they believe the original Bath stone was probably taken from for this building," he said.

After finding the stone, Barrow took it to a local stonemason who made it into the flooring.

Barrow decided to open them up during the renovation.

Now the fireplaces are filled with furniture.

"It was so overgrown that you could barely walk through," Barrow said.

It went on the market two weeks ago.

Barrow said he's already had a few interested parties and believes the home will sell soon.

Take a look at the listing here.

• Read more:
• My husband and I turned a dilapidated cabin into a dreamy beach house with virtually no DIY experience
  
• A Louisiana couple bought an 80-year-old general store for $55,000 and turned it into their dream home. Here's how they did it — and what it looks like now.
• 2 empty-nesters bought an abandoned farm in Pennsylvania for $220,000, and they've spent nearly 2 years and $150,000 renovating it. Here's what it looks like now.