In 1942 Townsville became a major military base, and a forts complex was built on Magnetic Island to spot aircraft with its two 3,000,000-candle-power searchlights. If you're going to do just one walk, then the forts walk (2.8km, 1½ hours return) is a must. It starts near the Radical Bay turn-off. Or head north to Radical Bay via the rough vehicle track. This has walking tracks to secluded Arthur Bay and Florence Bay (the northern sides of both offer the island's best snorkelling).