Question: What Fortress used as a palace and prison has the Festning tunnel running underneath it?

Context paragraphs:
Chris Pape: Chris Pape (aka Freedom) is an American painter and graffiti artist.  Pape started tagging subway tunnels and subway cars in 1974 as "Gen II" before adopting the tag "Freedom".  Pape is best known for his numerous paintings in the eponymous Freedom Tunnel, an Amtrak tunnel running underneath Manhattan's Riverside Park.  Prominent paintings in the Freedom Tunnel attributed to Pape include his "self-portrait" featuring a male torso with a spray-can head  and "There's No Way Like the American Way" (aka "The Coca-Cola Mural"), a parody of Coca-Cola advertising and tribute to the evicted homeless of the tunnel.  Another theme of Freedom's work is black and silver recreations of classical art, including a reinterpretation of the Venus de Milo and a full train car recreation of the icons ic hands from Michelangelo's Sistine Chapel.

Bjørvika Tunnel: The Bjørvika Tunnel (Norwegian: "Bjørvikatunnelen" ) is a motorway immersed tunnel on European Route E18 in the city center of Oslo, Norway.  The tunnel has two bores, with three lanes in each.  In the west, it connects to the Festning Tunnel at Akershus Fortress and runs under the Bjørvika arm of the Oslofjord before ending in an intersection on the east shore, where it splits into Mosseveien (E18) and the Ekeberg Tunnel (National Road 190).  The tunnel is 1100 m long, 675 meters of which run below sea level, and opened in September 2010.  It was built by the Norwegian Public Roads Administration The Bjørvika Tunnel is part of the Opera Tunnel complex which is the name of the interconnected system of tunnels between Ryen and Filipstad The Bjørvika Tunnel is the first immersed tunnel in Norway.

Akershus Fortress: Akershus Fortress (Norwegian: "Akershus Festning" ) or Akershus Castle (Norwegian: "Akershus slott" ) is a medieval castle that was built to protect Oslo, the capital of Norway.  It has also been used as a palace and as a prison.

Glion Tunnel: The Glion Tunnel is a two-gallery vehicular tunnel running underneath Montreux in Switzerland.  It carries autoroute A9, which links the Vaud canton to the Valais, and was placed in service in November 1970.  The tunnel is 1350 m long, 9 m wide and 7.5 m high.

Screaming Tunnel: The Screaming Tunnel is a small limestone tunnel, running underneath what once was the Grand Trunk Railway lines (now the Canadian National Railways), located in the northwest corner of Niagara Falls, Ontario, Canada.  The actual location of the attraction is just off Warner Road.  Often thought to be a railway tunnel, it was actually constructed only as a drainage tunnel so that water can be removed from the farmlands.  This water would go underneath the Grand Trunk Railway and down to the valley below.  Farmers used this tunnel to transport goods and animals safely underneath the busy railroad above.

Phoenix Park Tunnel: The Phoenix Park Tunnel is a railway tunnel in Dublin, Ireland.  The tunnel was built in 1877 and begins at the Liffey Railway Bridge near Heuston Station, running underneath the Phoenix Park for 690 metres before re-emerging close to the junction of the Cabra Road and Navan Road.  It joins with the Sligo line near Glasnevin, before continuing to Dublin Connolly.

Zoo York: Zoo York is a style and social philosophy inspired by the New York City graffiti art subculture of the 1970s.  Its name originates from a subway tunnel running underneath the area of the Central Park Zoo.  This tunnel, called the Zoo York Tunnel, or simply "Zoo York," was a haunt of very early "old school" graffiti writers who hung out with the hippies around the Central Park Bandshell in the late-1960s and 1970s.

Festning Tunnel: The Festning Tunnel (Norwegian: "Festningstunnelen" ) is a motorway tunnel on European Route E18 in the city center of Oslo, Norway.  The tunnel has two tubes, with three lanes in each.  It runs from Bjørvika, under Akershus Fortress, The City Hall Square and Vika to Filipstad.  The tunnel is 1800 m and -45 m elevation at the deepest.

Churston Court: Churston Court is the manor house of the former manor of Churston Ferrers (anciently "Cercetone" (Domesday Book, 1086), "Churecheton" (Book of Fees, 13th c.), "Churchstow", "Churchton", "Churchston", etc.), near Brixham in Devon and is a Grade II* listed building.  Today it serves as a hotel known as the Churston Court Inn.  It is located immediately to the west of the parish church of Churston Ferrers, also next to the former home farm, and about 1/2 mile south of the coastline at Elberry Cove, which intervening ground now forms part of Churston Golf Course.  It retains its original staircases, stone windows, oak panelling and flagstone floors.  The hotel has 19 en-suite rooms with four poster beds, and is said to be haunted by the ghost of a monk who appears in the old kitchen.  There is a smugglers tunnel linking the inn to Elberry cove, which lies about half a mile away.  There is also rumoured to be a link tunnel running over 10 miles to Berry Pomeroy from the inn.  These tunnels were driven more than 400 years ago, so the quality and stability of the passages are no longer known.  It is not known if the mine workings under Warborough Road, Churston contain any linking passages to the old smugglers tunnel due to the Warborough adits being untraceable or backfilled under overgrown thickett.  In a recent planning application regarding works at number 2 Warborough Road, it is documented that one of the deep shafts is capped underneath the property's garden.

Byfjord Tunnel: The Byfjord Tunnel (Norwegian: "Byfjordtunnelen" ) is a subsea road tunnel in Rogaland county, Norway.  The 5875 m long tunnel runs between Grødem on the mainland in Randaberg and the island of Sokn in Rennesøy municipality, running underneath the Byfjorden.  The tunnel was built as part of the Rennesøy Fixed Link project which opened in 1992 with the goal of connecting all the islands of Rennesøy to the mainland.  The tunnel was a toll road from 1992 until 2006.  The tunnel is part of European route E39 highway.  With a maximum 8% grade, the tunnel reaches a depth of 223 m below sea level at its lowest point.  The tunnel held the distinction of being Europe's longest and the world's deepest tunnel upon its completion, it was surpassed by a deeper tunnel in 1994 and a longer tunnel in 1999.  The tunnel had an average daily traffic of 9,675 vehicles in 2015.

Supporting paragraphs: Festning Tunnel Akershus Fortress
Answer: Akershus Fortress