The "Voyager"-class ships were the largest class of cruise ships in the world when constructed and were the first ships to have an ice rink at sea and the first to have Royal Caribbean's "Royal Promenade" mall concept, a main thoroughfare extending most of the length of the ship, flanked by bars, cafes, and shopping venues. They were built at Kvaerner Masa-Yards' (now Meyer Turku) facility in Turku, Finland. They have a gross tonnage of around 137,000 tonnes. Activity options onboard all five ships include a basketball court, at least three pools, a mini-golf course, a rock wall, an ice skating rink and, originally, an inline skating track. "Navigator of the Seas" replaced the inline skating track with a Flowrider surf simulator in 2014, and similar changes are planned for "Voyager" and "Explorer".