The Desvres Forest is near the French town of Boulogne. This postcard shows a shrine to the Virgin Mary, surrounded with candles, pictures, statutes and flowers.
The message on the back from "Harold" is written in pencil and reads: "A sample view of the interior of a wayside shrine. The building would be like an anti-chapel and unattended. This has more floral decoration than usual but generally speaking all village churches are much decorated."
The date at the top of the postcard reads 30.11.17, suggesting this postcard was sent in 1917, during the First World War. There's no stamp, and no mark suggesting one was ever attached.
It's difficult to read the name of the addressee, but the address itself appears to be Bank Street, Ipswich.