Mumbai is truly blessed to have such a great wonder of the World Gilbert Hill  right in its midst. 

 Gilbert Hill: A Lava Wonder. ... Hidden in Mumbai's suburb, Andheri, Gilbert Hill is a 200 ft (61 m) monolith column of black basalt rock. It was formed when molten lava was squeezed out of the Earth's clefts during the Mesozoic Era about 65 million years ago and the basalt found around the area are of volcanic origin

Arguably the oldest heritage site in the country in its origin.  A few temples and gardens are at the top of the hill. Plans are afoot to make it a tourist attraction spot with a high speed elevator to take the visitors to the top.  Gilbert Hill In Andheri Is One of The World’s Only Three Oldest Things Still Battling Time: 

River March has been striving with the Government official to take all steps to ensure that this great heritage structure is protected