Doubtful Sound is a very large, U-shaped fjord within Fiordland National Park (New Zealand). Doubtful, Milford Sound and Dusky Sound are among NZ's most-popular cruise ship travel destination. Doubtful Sound has total length approx 40 km (25 ml), ranking it Fiordland's second longest. Its max depth is 421 m (1381 ft). The nearest town (Manapouri) is at approx 50 km (31 ml). Fjord's scenery features surrounding high mountains (with peaks reaching up to 1,6 km (5200 ft) covered with dense rainforest, steep hills, hundreds of waterfalls (the largest being Helena Falls and Browne Falls, over 600 m / 2000 ft high). Wildlife includes bottlenose dolphins, fur seals, penguins, large whales (humpback and right whales, minke whales, sperm whales, beaked whales, pilot whales, orcas), starfish, corals. Doubtful Fjord is designateded"Important Bird Area" for being breeding ground for Fiordland penguins.