Panama City is supposedly the oldest European settlement on the Pacific Ocean. It was founded in 1519. Unfortunately, it was destroyed by captain Henry Morgan in 1671, and the capital moved to what is today known as Casco Viejo in 1673.
Visiting the ruins of Panamá Viejo, as the original capital is known, is fascinating. It was frigging hot and humid, and the place is kind of big. But I still enjoyed walking around this ancient former capital sitting next to mangroves, half-conquered by nature, with the occasional glimpse of modernity from behind the ruins...
The tower of the cathedral still stands tall, and is in fact on of the best known symbols of Panama. You can enter and climb it to the top, from where you can have more interesting views from the modern city in the distance.
Finally, Panama's mudflats. You can see them during your visit of the ruins. They're rich in nutrients and numerous birds and crustaceans feed on them. A curious sight.
I didn't see many tourists around, but I think this is really a must if you visit Panama. I mean, this is the very first incarnation of the capital!