Off the coast of St. Petersburg, Russian in the Gulf of Finland sits the abandoned Fort Alexander. The fort was built in the mid-1800s to protect the waterway around the then capital city. Though never involved in direct military action, it was used for strategic purposes such as setting up mine fields and ammunition storage.
As the 1900s approached, the Russian government found another useful purpose for the fort. Given its isolated location, it would become the ideal base for bacterial research for the newly formed Institute for Experimental Medicine (tell me that doesn’t sound ominous). Fort Alexander was renovated, creating research laboratories, a science library, animal enclosures for camel & reindeer (you need test subjects), and a crematorium (you need to dispose of your test subjects). The main focus for the new facility was the study of the plague and the creation of a vaccine. It was because of this focus that it earned the nickname “The Plague Fort”. They also worked on other diseases such as cholera, tetanus, typhus and Streptococcus. When the Communist Party took over Russia in 1917 operations were terminated at the fort and moved to the mainland.
The fort spend time during the rest of the 1900s as storage facility and repair shop but was completely abandoned in the early ‘80s. In the late ‘90s and early ‘00s it became a popular location for raves.
For an even creepier abandoned labratory, check out this one appropriately nicknamed "The Horror Labs."