Exploring an underwater tunnel at Akershus Fortress

Monday, November 7, 2016 / Akershus Fortress, Oslo, Norway

Words by Ronny Arnesen / Cave diver and explorer

For about 17 years ago the assignee heard rumors of a well at Akershus Fortress that was suppose to be an escape route out of the fortress. This of course excited my curiosity, but other the project drowned cause of too many other exciting projects.

Later in 2016, Arnar Snorrason came in contact with Tom Andersen after an excursion to the fortress by Oslo Fire Department. This lead to a project about exploring the rumors about the escape tunnel.

In the archives of Akershus Fortress, there is a report that is presenting an examination that was published in the local newspaper in August 1864. This report gave an impression about how big this tunnel system could be. But still, many questions remained to be answered. Was it possible for us to explore the tunnel again today with better technology? - We decided to give it a try.

This is a summary of the Norwegian report "Utforsking av brønnen ved Jomfrutårnet" by Ronny Andersen. Fin the Norwegian report here. This is an extract of the daily log from September 12th 2017, where Blueye was a used as a tool to explore the hidden tunnels in the well.

A map of the system as it was known after exploration with divers February 28th, 2017. Drwaing: Arnar Snorrarson, Rolf Kolstad and Ronny Arnesen

By the well house, we get ready to deploy the Blueye underwater drone (mini ROV), with support from Martin Ludvigsen from Norwegian University of Science and Technology (NTNU)

The ROV is lowered into the well. Foto: ROV Martin Ludvigsen/NTNU, Blueye Robotics

With calm movements, Martin drives the drone into the tunnel. It's pitch dark, but with the bright lights of the drone it is possible to get a good overview of the first room. The drone is approaching the narrow opening and the excitement is increasing as we start to enter the narrow passage into the next section.

The aquatic drone is on its way to the narrow passage in the well. In the end of the first room the narrow passage appears. Foto: ROV Martin Ludvigsen/NTNU, Blueye Robotics

There is a color difference on the wall that is showing that there might have been lower water level in the past. Foto: ROV Martin Ludvigsen/NTNU, Blueye Robotics

Martin aims for the hole and flies through it. As the drone enters the new room, the visibility decreases, but it does not take long before we recognize that this room is much larger than the previous one. The floor and walls are gradually floating into each other, so it's hard to tell where the wall ends. But as the drone continues into the room, the walls come closer and form a narrow tunnel again.

In the middle of the bigger room, there are some loose stones that probably have fallen down from the roof. Foto: ROV Martin Ludvigsen/NTNU, Blueye Robotics

After driving a couple for more meters, the tunnel is sealed with broken pieces of pipes and Tiling stones. The Blueye Pioneer has fully discovered new territory that had been inaccessible for many hundred years.

A pice of broken pipe in the end of the tunnel. Foto: ROV Martin Ludvigsen/NTNU, Blueye Robotics

The end blockage of the tunnel. Foto: ROV Martin Ludvigsen/NTNU, Blueye Robotics

The drone turns around, and follows the yellow tether back to the entrance of the tunnel system.

The Blueye Pioneer has fully discovered new territory that had been inaccessible for many hundred years. This project could not have been more successful!