Longest videogame marathon on an action-adventure game

According to Official Guinness Records,

The longest marathon playing an action-adventure videogame lasted 109 hours exactly and was achieved by Tony Desmet, Jesse Rebmann and Jeffrey Gamon (all Belgium) who played Assassin's Creed: Brotherhood (Ubisoft, 2010), at the GUNKtv World Record Gaming Event in Antwerp, Belgium, from 18 to 22 December 2010.
The record attempt started with 20 participants. The three record holders were the only ones who were able to survive to the end.

For a complete list of 2010 records, please visit 2010 Guinness Records in Belgium.

Other Belgium records that might interest you:

• Most lights on a Christmas tree
• Brightest digital cinema projector
• Most valuable advent calendar
• Largest pop up book
• Largest attendance at a tennis match