In the morning, take a romantic stroll along the Arabian sea shore from the iconic Gateway of India, one of the most photographed landmarks in Mumbai. You can then take a ferry to the Elephanta Caves, a UNESCO World Heritage site, to explore the ancient rock-cut temples dedicated to Lord Shiva. In the afternoon, head towards the Chhatrapati Shivaji Maharaj Vastu Sangrahalaya museum, which has an impressive collection of Indian art, history and culture from the ancient to modern times. In the evening, visit the Marine Drive promenade, also called the "Queen's Necklace" because of its stunning night view of the streetlights that resemble a necklace.
Start your day with a visit to the Sanjay Gandhi National Park, one of Asia's most visited parks. It has a rich flora and fauna, including leopards, lions, deers, and over 200 species of birds. You can take a safari tour or hike to the Kanheri Caves, a group of rock-cut monuments and Buddhist shrines dating back to the 1st century BCE. In the afternoon, head to the Juhu Beach, one of Mumbai's most popular beaches, to enjoy some local street food and watch the sunset. For the evening, take a romantic walk along the Bandstand Promenade, a 1.2 km long walkway along the sea that has stunning views of the Worli Sea Link.
If you have some more time, you can also visit the Haji Ali Dargah, a mosque and tomb situated on an islet in the Arabian Sea, or the Siddhivinayak Temple, one of Mumbai's most famous and auspicious temples. For side trips, you can explore the Elephanta Island and the Kanheri Caves or take a day trip to the hill stations of Lonavala and Khandala. To maximize your fun, you can try some local street food and shop for souvenirs in the Colaba Causeway market or the Crawford Market. For any other suggestions and tips, feel free to ask your local tour guide.