I'm not aware of any water nearby the building. It's a short tour and the time depends on how long you take to read the info at the exhibits. I'd say an hour maximum.
Yes, there is water access about a mile down the road.
The tour of the museum in the Black Water Refuge is a beautiful& educational trip back on time to a regrettable time in the history of the USA but, like the Holocaust Museum, brings it to life so we don't forget the harsh life the people who were affected by the ignorance and hatred of those under Satin's power. Rest rooms & drinking water are provided & donations accepted. The UGRR route extends from Vaginia to New York. There are several good books about it & Tubman's life.
It is , generally, within the Blackwater Refuge which is a marshy area. So, it depends on what you mean by water access... It is relatively close to Cambridge and the Choptank River.
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