This is one of those fascinating finds you personally discover, as it is hardly marketed/ promoted...
Murud is a rocky beach naturally & with rock sediments mixed in the sand, it appears naturally greyish-black & the sea is exceptionally saline.
But what strikes you most is Shivajis fort right in the middle of the sea - majestic & breath-taking.
Soaked in heritage, another fort in the sea - the Janjira fort - built by the Nawab (& that could never be captured) is an exciting trip with a 15min sailboat-ride. Tho vandals have created a mess of the fort runis inside, its definitely worth a visit.
If in Murud, strongly recommend the Golden Swan Resort - comfortable cottages & a chef youd want to take home!
If you are travelling from Mumbai, Id recomm taking a catamaran from Gateway, followed by a 1hr Vikram ride from Alibaug -- a mundane road trip all the way from Mumbai leaves out a lot of the excitement.