In between the Rockaway Peninsula and the "mainland" of Brooklyn lies both land and water that are part of Gateway National Recreational Area which is operated by the National Parks Service (NPS). Many people are usually surprised to find out there is National Park area in NYC but Gateway is often among the top 10 most visited National Park areas annually. While this Brooklyn/Queens area is the largest swath of NPS area in NYC, Gateway extends to areas in Staten Island and New Jersey as well. The full list of Gateway Parks includes:

Brooklyn
Canarsie Pier | Floyd Bennett Field | Jamaica Bay Wildlife Refuge

Queens
Breezy Point | Fort Tilden | Jacob Riis Park

Staten Island
Fort Wadsworth | Great Kills Park | Miller Field

Monmouth County, New Jersey
Fort Hancock | Sandy Hook

As a National Park area, most of Gateways areas and activities are low cost or free and open to the public.

Here are a few "must-dos" if you want to get out to a National Park on a Saturday afternoon (or evening):

1) Camping 

There are campsites at Floyd Bennett Field in Brooklyn, Fort Wadsworth in Staten Island, and Sandy Hook in New Jersey (accessible by ferry from midtown).

2) Kayaking

There are a number of free paddling opportunities throughout Gateway operating throughout the summer. Pro-tip: show up early to make sure you get a spot. Alternatively, the Sebago Canoe Club offers low cost paddling every Saturday.

3) Fishing

For recreational fishers you can actually obtain a permit from the DEC to be able to fish in much of the water of the area. But make sure to read the health suggestions on eating fish from the area.

4) Go for a bike ride 

Bring your bike along to explore the bike paths in Fort Wadsworth or hit various Gateway sites with the 19 mile loop around the Jamaica Bay Greenway. 

5) Birding & Beaching

Mix a beach day with bird watching at Breezy Point in Queens.