Eastern State Penitentiary, Pennsylvania, USA
When notorious criminals such as Al Capone and Willie Sutton were held there, you know you have a historic landmark in front of you. Operational until 1971, it was famous for its solitary confinement system: inmates lived alone, ate alone, and were even hooded whenever they had to leave their cell. As with most abandoned places, it has been transformed into a haunted house, and its authentic environment makes for an instantly immersive experience.
I was there ... awesome
My dad, his brother, and dearest friend all worked the Queen for decades, over 75 years combined. Worst horror related by all of them was from the very much alive people, not a single one reported anything erie about it.
Ripper tour - find one that is led by someone who has written books or done professional studies on the subject, I had a great time!
Tower of London - surprised to find it wasn't just a single tower but the entire complex. One of the Beefeaters that gives tours is a retired Royal Marine and stand-up comic, he was educational and absolutely hilarious!