At not cost this is definately in everyone's budget, however many fail to go up the mountain and miss these phenomenal views.
Whether you're a hiker, jogger, walker or just out for a pleasant car ride, the Tantalus and Round Top Drive is the perfect place to spend a few hours. The views of Diamond Head, downtown Honolulu and Punchbowl Crater (military cemetery -- a very educational visit) are fantastic. If you're lucky enough to be on the mountain at sunset, the views of the city's lights are amazing.
The road Round Top Drive is a nine-mile loop and is very pretty in of itself, so do take your time on the drive.
Along Round Top Drive, you will find the entrance to Puu Ualakaa Park
Less than a half mile further along the road you will come to the entrance to Puu Ualakaa Park. This park contains the best views from Mount Tantalus. In the movie Blue Hawaii, this is where Elvis Presley and his girlfriend went for a picnic.
The overlook at Puu Ulalakaa Park offers a panoramic view of southern Oahu from Diamond Head to your left, through Waikiki, downtown Honolulu and to Punch Bowl Crater and the Honolulu International Airport beyond on the right.
Take special care of your car and belongings at this park. The forest borders the parking lot and car break-ins have been known to occur.