At the Lanai Lookout, on a clear day, you can see all the way to Mount Haleakala on Maui. Most days, you can certainly see Lanai, if you know what to look for.
There is a hidden gem at this location. It is home to one of the few lava tubes left on Oahu which is easily accessible. Do a little exploring to find yourself go through this historic piece of the island, under the road and overlooking the Pacific.