Wilbury Hill Camp is a late Bronze Age hillfort west of Letchworth. The earthworks are subtle rather than spectacular, but they add a much older layer to a town usually discussed through 20th-century planning.
It is worth seeking out if you are walking the western edge of town or have an interest in prehistoric landscapes. Do not expect a reconstructed site; expect low banks, open ground, and the satisfaction of standing somewhere people were organising and defending long before the garden city was imagined.