It's easy peasy to bicycle in Brooklyn. You can ride through Prospect Park, a beautiful park. You can use the bicycle path along Eastern Parkway, along Ocean Parkway, along the Promenade, go over the Brooklyn or Manhattan Bridges, the boardwalk at Brighton Beach and Coney Island, Shore Road along Narrows Bay, or just go down city streets to wherever you like.
Bicycling is easy in NYC because the parked car lane is usually 1.25 lanes wide, so except for doors opening, it is very easy to be out of the way of traffic.
I have been bicycling for years in Brooklyn, even down Flatbush Avenue, the biggest heaviest-traffic commercial street, even at night. And I've been on it from the Manhattan Bridge all the way to Kings Plaza and the Rockaways. The city is so lit up, it's not that hard or scary (automobile-wise or people-wise).
The toughtest part is that Eastern Parkway is the top of ridge along the highest part of Brooklyn, so that riding from Cobble Hill to Prospect Park is uphill, and going from Flatbush north up to Eastern Parkway is also uphill.
If Dyke Hts is, lets say 7miles from where you are to Dyker Heights, it would take AT MOST an hour to get there. You can go straight down any of the numbered avenues.
Finally, if it's dark and late, and you're tired, just take the bicycles on the subway. There are no legal restrictions.
You can get the Hagstrom Pocket Atlas of New York City, and look through the pages for Brooklyn.
