Complex sentence: In the late 1980s, a second phase of development was being designed for Disneyland Paris (then Euro Disney), including was a free fall type ride in Frontierland that was to be named Geyser Mountain.
Split into simpler sentences: In the late 1980s, a second phase of development was being designed for Disneyland Paris (then Euro Disney). Included was a free-fall type ride in Frontierland that was to be named Geyser Mountain.