Officially the Kaiwa Ridge Trail, the Lanikai Pillbox Hike is the most popular short walk on the windward side and one of the best sunrise spots on Oahu. The trail climbs steeply up the ridge directly behind Lanikai and reaches the first of two WWII-era concrete observation bunkers in about 20 minutes. The view from the top is hard to beat: Lanikai and Kailua beaches below, the Mokulua islets straight ahead, and the Koolau range curving away to the south.
The trail is short — about 1.5 km each way — but the first section is steep, exposed, and slippery when wet. Bring water, wear shoes with grip, and avoid it in heavy rain. Park on the public street, not in the residential areas behind Lanikai, where parking is restricted.