Many medieval castles had escape tunnels for when the castle was under siege. Manorbier Castle in Wales has an escape tunnel entered through the well. I used this detail from Manorbier and my experience of spending 12 hours in an old lead mine in Cumbria in my first novel, Almodis the Peaceweaver (Impress Books, 2015). In the novel, Almodis and her friends escape from a besieged castle through just such a tunnel.
Breze castle in the Loire valley, close to Fontevraud Abbey, has an extensive underground refuge, which probably dates back to the time of Viking raids up the river.
With no bank vaults and safety deposit boxes the best way to hide your ill-gotten gains was to bury them underground, hence the many spectacular Viking hoard finds.
Roman and medieval mining and underground mine networks are a fascinating topic. My most recent novel, The Anarchy (Impress Books, 2020), features the Roman gold mines at Dolaucothi in Wales. In my descriptions of medieval mining I drew on Georgius Agricola’s 16th century book De re metallica. I was introduced to this book by my friend, Alan Smith, who was also one of the people I spent 12 hours underground with in the old lead mine in Cumbria. More on that experience here including my text, Silent Running.
To celebrate World Book Day my publisher, Impress Books, are offering 10% discount throughout March on books purchased from their website or you can choose instead to have them donate a book to a charity working with refugees.