As of the early 21st century, the only regular traffic on the river within the city is the Liffey Voyage water tour bus service, which runs guided tours along the River Liffey through Dublin City centre. Departing from the boardwalk downstream of the Ha'penny Bridge, the Spirit of the Docklands was built by Westers Mekaniska in Sweden as a 50-passenger water taxi. Its variable ballast tanks (not unlike a submarine) and low air draught mean that at low tide it can float high, but at high tide it can ride low and still pass below the Liffey's bridges.