The fortified walls of Hurst Castle have helped it withstand the test of time. Admire the architectural features of this grand building from afar or see if there are any tours.
You're spoiled for sightseeing choice when in Lymington. Hurst Castle is a good place to kick off here, but there are numerous other interesting spots to enjoy. Milford on Sea Beach, Colwell Bay Beach, and The Needles are near the fortified complex and will round out your day nicely.