This page of our Assassin's Creed Valhalla River Raids guide explains what river map clues (Saint George's Clues) are and what they are used for in the game.
Saint George's Clues - where to find them?
While raiding the surrounding settlements, you may find two Saint George's clues. They are hidden in monasteries - one near the Exe river, the other near the Severn river.
You simply have to explore the area well in order to get them. It is recommended to use Odin's Sight to make it easier to find your way around.
You cannot summon a raven in raiding areas. If you want to find out more, take a look at Raven - why can't I use it?
Unlocking the third map
After getting both Saint George's clues, you must return to Vagn. He will then give you access to another raid map. Thanks to it, you will gain more raw materials, secrets and treasures.
We have dedicated separate pages to all the secrets added in this update: