The Alter Elbtunnel (also Old Elbe Tunnel, St. Pauli Elbe Tunnel) is a pedestrian, bike and motorist tunnel, which travels underneath the River Elbe and connects central Hamburg to the southern side of the river. While walking, be sure to look at the artworks that line the tiled walls. Travelers enjoyed the experience of walking beneath the river and taking in the great view from the opposing side. Free of charge for pedestrians and bikers, motorists are charged a small fee. You'll find the Elbe Tunnel open 24 hours a day (for pedrestrians/bikers) off the Landungsbrücken U-bahn stop.

Planten un Blomen (translates as the very imaginative Plants and Flowers), but creative name or not, this park is a favorite among travelers. In the summers it features a light, water and music show; in winters, the park unveils an ice skating rink. And amongst the many different flowers, trees and plants to enjoy, kids can also play at the playground. You can get here off the Stephanspl U-bahn stop, and enjoy Planten un Blomen for free.

All-night revelers finish up their partying at the Sunday morning St. Pauli Fischmarkt (Fish Auction Hall and Market). Not only are there stalls brimming with fresh fish and other goods, but there's also steaming hot bratwursts, free flowing beer and even an energetic band to keep the jovial atmosphere alive. If you sleep in (or you're just getting to bed after bar hopping), you'll miss out on the Fischmarkt; it's open on early Sunday mornings only.

Travelers really enjoyed the Fischmarkt, saying it was a one-of-a-kind, colorful and rambunctious experience. It's also one of those uniquely Hamburg attractions.

The red-brown buildings of the Speicherstadt (Warehouse District) used to shelter the city's imports -- coffee, spices, silks -- which were carried fresh off the boats in the harbor. Although these buildings aren't open for tours, travelers are fond of snapping pictures of this historic area. You'll find it off the Meßberg U-bahn stop.

Hamburg's Reeperbahn rivals Amsterdam's Red Light District for its magnitude. Located in St. Pauli, the Reeperbahn is a corridor of sex shops, strip shows and brothels. And although the street is free to tour, any of its shows and "services" are very expensive. Some TripAdvisor users specifically note the Reeperbahn's seediness, drunks and even street fights.

But the area in and around the Reeperbahn is also the site of much of Hamburg's nightlife, from pubs to clubs and theaters too. You can tour this area by hopping off the St. Pauli U-bahn or the Reeperbahn S-bahn stations.