Whenever you book a local tour, sightseeing or even just tickets to museums, cable cars etc, it's almost always cheaper to book online. Plus you don't have to deal with touts or stand in long queues, or worse, refused entry because of sold out activity. Viator and Klook are two of my favorite platforms to book such activities online. They are much simple to use and have almost every activity covered across all major tourist cities worldwide.
And if you book the same activities via IHG, you also get an additional 1000 reward points on every booking. I can easily see myself earning enough points for a free stay on every trip.
You can see the bonus reward points on the activity details page