In the YouTube video titled "Secret Government Project: Entryway," former US Air Force member Joshua A. Jameson shares his experiences as a volunteer in Project Entryway, a lesser-known sister project of the infamous Montauk Project. He joined the project around the late 1980s, drawn by a military mission requiring medical and security personnel. Upon entering the facility, they were unaware of Montauk's notoriety and believed it to be just another radio site. Jameson and his team were led to a massive concrete room with magnetic locks and observation decks, where they provided security and potential search and rescue operations. They were told to keep the project a secret and were introduced to scientists from Brookhaven Laboratory. The team's mission was to explore the unknown, and they encountered a shadowy black void leading to another plane of existence. Dr. Carter, the exploratory scientist, led the team through the gateway, but during an experiment where he stepped through for an extended period, he disappeared, leaving his team to search for him in the unfamiliar world. The team later discovered that Carter had been missing for nearly four days on his end and had encountered strange beings. As the team continued their experiments, they encountered violent events, including the death of their team members and their own exposure to unknown substances that granted them superhuman abilities. The speaker, who is leading the team, expresses regret for his actions and acknowledges the potential consequences of the experiment.