The Södertälje Canal connects Lake Mälaren to the Baltic Sea at the point where the two bodies of water naturally came closest, and the lock here is the largest in Scandinavia. Cargo ships, tankers, and pleasure boats pass through continuously throughout the year. The towpath along the canal is a pleasant walk, and you can watch vessels locking through from the bridge directly above the gates.
The surrounding waterfront area has been tidied up in recent years and makes for a good stroll. There is a small exhibition about the canal's history near the lock. The canal is an active working waterway, not a heritage attraction — which makes it more interesting.