From A Wiki of Ice and Fire
Old Oak is the seat of House Oakheart. It is located in the west of the Reach near the Sunset Sea, along the Ocean Road which links Highgarden and Lannisport. Old Oak's maester is Omer.
The petty kings of House Oakheart joined the Kingdom of the Reach, the realm of King Garth III Gardener, through a pact of friendship and mutual defense. Lancel I Lannister, a King of the Rock, conquered as far south as Old Oak before being killed in combat, and his gains were lost by his son, King Loreon III Lannister.
There are tapestries at Old Oak that show historical conflicts between the Oakhearts and Dornishmen. The infamous actions of the Wyl of Wyl are still remembered at Old Oak.
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