If fancy a dip the sea here are some good beaches for swimming: 

Kilclief - just down the road from Strangford this is an easily accessible beach that is safe for sea swimming.  (Pictured)

Helens Bay - If you are in Belfast then Helen's bay will be your nearest spot for swimming.  This beach will have swimmers in no matter the weather and is one of the most popular places for sea swimming. 

Climb Slieve Donard, the highest mountain in NI or just admire the view from the coast.  Either way the Mournes are a must see in County Down as one of the most beautiful sights in the country.  They stretch along the County Down coast providing breath taking views from every angle.  You can visit Tollymore Forest Park in Newcastle and go for a walk without having to climb an actual mountain if that helps.

Dundrum has great views of the Mournes, a castle and the Mourne Seafood Bar if you fancy ticking several things off at once.  

A world of wetland nature awaits you at Castle Espie Wetland Centre run by the Wetland Wildlife Trust.  Castle Espie is a wetland nature reserve that is home to wonderful birds and wildlife.  It is on the shores of Strangford Lough and it is hailed as an international exemplar of best practice in habitat restoration, sustainable design and green tourism.

Pretty much everywhere in Norn Iron counts as "Nature" so you won't be short of walking routes or beaches to visit or open green space in general.  Rather than list every place in the entire county we chose the ones that would appeal to most people, so if you are looking for recommendations for a specific area or want to go somewhere good for cycling etc let us know and we can recommend where is best! 

Bangor/Donaghadee are your best bet for water related activities.  Paddle boarding, sailing and water skiing etc are all available around the top of the peninsula. 

You will find lovely beaches, quaint harbours and gorgeous open sea along this part of the coast if you are looking for more adventurous activities.