Bring an umbrella? But seriously, there are still plenty of options in Sandusky even if it's wet. In fact, you can still get wet inside with several big indoor water parks like Castaway Bay and Kalahari, which both offer day passes for non-resort guests. For more ideas about activities in the area, both indoors and out, check out this link: http://www.shoresandislands.com/visitors/do/activities/