Walk Inside the 19 UNESCO Windmills (the whole reason the port exists)
This is THE iconic Dutch landscape: 19 monumental 1700s windmills marching across green polders below sea level, the largest concentration on earth and a still-working 1740s flood-control machine. Your single entry ticket isn't just the view from the dike (that part is free) — it unlocks climbing inside the working Nederwaard mill (1738, original machinery and the Hoek family's preserved living quarters) and the rare hollow-post Blokweer (1630, set as a 1950s miller's home with goats and a costumed miller), PLUS the hop-on/hop-off canal boats that glide you down at water level with mills towering on both banks, the Wisboom pumping station and the exhibitions. A first-timer who only saw this from the ship rail would genuinely regret not walking it.