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The Gatún Locks, 10km south of Colón, raise southbound ships 29.5m from Caribbean waters to Lago Gatún. Just the size of them is mind-boggling. In The Path Between the Seas, David McCullough notes that if stood on its end, a single lock would have been the tallest structure on earth at the time it was built, taller by several meters than even the Eiffel Tower. Each chamber could have accommodated the Titanic with room to spare.

Workers poured a record-setting 1,820,000 cubic meters of concrete to construct the Gatún Locks. The concrete was brought from a giant mixing plant to the construction site by railroad cars that ran on a circular track. Huge buckets maneuvered by cranes carried the wet concrete from the railroad cars and poured it into enormous steel forms. Locomotives moved the forms into place. This protracted process continued virtually uninterrupted for four years until the Gatún Locks were completed.

A viewing stand opposite the control tower offers a prime view of the locks in action. The two-hour process is the most interesting stage of the canal transit and the English brochure clearly describes what you’re watching.

Once the ships pass through the locks, they travel 37km to the Pedro Miguel Locks, which lower southbound ships 9.3m to Lago Miraflores, a small body of water between two sets of Pacific locks. Ships are then lowered to sea level at the Miraflores Locks.

Buses to the Gatún Locks leave the Colón bus terminal hourly (US$1.25, 20 minutes). If you arrive by taxi you can stop here before heading on to Gatún Dam – another 2km away. A taxi ride from Colón to the locks and dam and back should cost US$60 per party, but agree on a price before leaving.