Sadly, the closer you are to the Equator, the warmer it gets!😬 That said, choose your tours wisely ~ The Cartagena tour we did started nice & early going to the fort (a blessing) it does require a trek up a steep hill, (should you choose to go up). When we were in the Old Town we tended to be in & out of various buildings, so it really wasn’t all that bad. We also opted to omit going to an Emerald Museum (there are a few) and wandered down a street to a small pastry/coffee shop & enjoyed some local food. We then wandered to a nearby square where we enjoyed a cool drink and returned to meet up with the group. Yes it was hot, but not unbearable. I’m sure you’ll enjoy it all & if you’re on Ruby, it’ll be the best!