The Olympics DLC would add a bunch of sporting arenas as well as a Summer and Winter Olympics you could trigger.
This DLC would add some simple sport venues as well as some arenas, which would be a bit larger, more expensive, but have increased recreational effects as well as being able to produce money by changing ticket prices.
Some smaller sport venues that could be added:
Ice rink
Track course
Baseball
Some arenas that could be added:
Soccer arena
Aquatic-ice arena
Course arena
Basketball arena
Multipurpose arena*
Ski resort (lift ticket prices instead, requires a certain slope)
Artificial ski resort (same as above but more expensive and no slope requirement)
In order to trigger the Summer Olympics event, on would need: Soccer arena, Aquatic-ice Arena, Course arena (track+equestrian), Basketball Arena, or a Multipurpose arena which could be given upgrades to fill in for any three of these at once but is bigger more expensive.
In order to trigger the Winter Olympics, one would need:
Track course (bobsledding???)
Aquatic-ice arena
Multipurpose arena (fills in for both of these)
Ski slope of some kind.
The corresponding olympics event could then be triggered during the appropriate season. The events would cause a massive boost to tourism for a week, a permanent boost the tourism, and an increase in demand for a few weeks.
This might need balancing, but I think it would be a neat idea and add some cool buildings to add to your city.