10 Horrifying Serial Killers You've Never Heard Of

2. The Murder Castle

In 1886 Dr. H. H. Holmes, an affluent Chicago pharmacist, purchased a drug store in Chicago, buying up property around it over the following months until he owned the entire block, which was painstakingly remodelled into a hotel. Holmes' hotel was opened in time for the 1893 World's Fair, which gave the new building its name: the World's Fair Hotel.

Unbeknownst to the men and women who'd worked on the project, this was more than just a hotel.

Holmes, whose real name was Herman Webster Mudgett, was a sadistic psychopath, and he'd carefully had the building designed and built to his specifications. The workers had worked on small pieces of the building each, and all were sacked before their part was completed: no one except for "Holmes" was ever able to see even a fraction of the complete picture.

The World's Fair Hotel was a horror house, created for torture and murder. Most of the rooms had no windows, while several doors and stairways went nowhere and some hallways were dead ends.

One room was reserved for hanging, one cell lined with brickwork earmarked for his victims to die of hunger or thirst. Blowtorches were built into the walls of some of the rooms and gas jets into the walls of others, while a chute led from the upper floors to the basement. That basement contained two furnaces big enough to incinerate multiple corpses at once.

Holmes would take advantage of the influx of tourists and new citizens brought in by the World's Fair to entice young men and women back to what would later become known as the Murder Castle. He'd torture, mutilate and kill dozens before he was caught: because the remains were thoroughly disposed of in the ovens, or in lime pits or by acid - some remains even sold on to medical schools - the full body count couldn't be proven.

Nine murders were forensically confirmed from what little physical evidence was found after the Castle was ransacked by police. An inveterate liar and fantasist who claimed to be a vessel for Satan himself, Holmes initially confessed to killing 100 people, then confessed to killing 27 people, then 30 and finally claimed only two, but the estimates place the real total as potentially over 200.

Holmes was convicted and hanged in May 1896: the noose didn't break his neck, leaving him to slowly asphyxiate over the next fifteen minutes.

The hotel itself was mysteriously gutted by fire the year before he died, and the shell of the building demolished a few decades later: it's now the site of the Engelwood branch of the US Postal Service.