Great Bay Discovery Center is the visitor-facing part of the Great Bay National Estuarine Research Reserve, about a short drive inland from Portsmouth. The center introduces the estuary's salt marshes, mudflats, tidal rivers, eelgrass beds, and bird life, then lets you step outside onto trails and boardwalks where the landscape explains itself better than any display panel can.
This is a good stop for travellers who want the New Hampshire coast without another busy beach town. It is especially useful with children, birders, or anyone curious about the tidal ecosystem behind Portsmouth's harbor. Check seasonal opening hours for the building, but the reserve lands and trails are the larger reason to go.