Exit the garden from the exit facing Bedford Street and turn left. When you reach Chandos Place, turn right. You should soon reach William IV Street, where you'll find the Edith Cavell Memorial.
On each side of the base, you'll se a different word, for a total of 4 words.
Put the 4 words in alphabetical order, then type them in the Enter solution box separated by a / (no spaces). This will take you to your next challenge!