Hellevoetsluis was designed as a fortified naval base, and its star-shaped earthwork fortifications survive largely intact — an increasingly rare thing in the Netherlands, where most fortifications were demolished during 19th- and 20th-century urban expansion. The circuit of the walls takes about 30–40 minutes to walk at a relaxed pace, with good views over the harbour basin and out toward the Haringvliet.
The ramparts are grassy and publicly accessible. In summer they are a pleasant place to picnic or cycle; the full circuit on a bicycle takes about 15 minutes. The design is classic Dutch military engineering of the 17th century — low, angled bastions intended to deflect cannon fire rather than simply withstand it. Several of the original gates and sluice structures remain in place.