Sure, here's an ideal itinerary for one day in Mangalore:

Morning: Start your day with a visit to the famous Kadri Manjunath Temple. This temple is dedicated to Lord Shiva and is one of the oldest temples in the city. The temple has a beautiful architecture and is surrounded by lush greenery.

Afternoon: Head to the St. Aloysius Chapel, which is located in the heart of the city. The chapel is known for its stunning frescoes and paintings that adorn the walls and ceilings. It is a must-visit for art lovers.

Next, head to the Panambur Beach, which is one of the most popular beaches in Mangalore. You can relax on the beach, take a dip in the sea or indulge in some water sports activities like jet skiing and parasailing.

Evening: Visit the Tannirbhavi Beach, which is another beautiful beach in Mangalore. The beach is less crowded than Panambur Beach and offers a serene atmosphere to unwind and relax.

End your day with a visit to the Gokarnanatheshwara Temple, which is located in Kudroli. The temple is dedicated to Lord Shiva and is known for its grandeur and beauty. The temple is beautifully lit up in the evenings, making it a perfect place to end your day.

Hope you have a great time exploring Mangalore!