These days, Portobelo looks like a small village set at the end of a swampy, well-protected bay off of the Caribbean. Because of this sheltered harbor, Portobelo has been around since 1597 when it was a major shipping port along the Spanish Main. It was so important and wealthy that most everyone of note attacked it. Portobelo was captured and at least partially destroyed in 1601, 1668 and 1739. After that the overland route across Panama became less important and Portobelo reverted to a sleepy edge of the jungle sort of place.
There are three forts left over in Portobelo, they are all relatively small and in various stages of decay. If you're arriving from Sabanitas (which is nearly guaranteed), the first fort you'll reach after driving along the harbor is Fuerte Santiago. It looks about like this, if you happen to visit on a very rainy day.
Some cannons are left pretty much where they were when the Spanish abandoned the city. The ramparts have a scenic view of the bay and the town. We arrived the day before the peak of the Black Christ festival which is the major event in Portobelo annually. It involves a pilgrimage to the town and a visit to the cathedral to see a somewhat mysterious artifact that has no particular story attached to it. (Seriously, if you ask around you'll get a completely different story about it from every person).
Given the amount of visitors to the town during the Black Christ Festival, we parked out by Fort Santiago. Portobelo is so small however this is not really a big deal. Nothing in town is a particularly long walk from anything else in town. As for the pilgrims walking to Portobelo from Sabanitas (and beyond), there are aid stations set up periodically along the route. Pilgrims are distinct due to purple garments they wear.
Portobelo has a central square, a short commercial strip along the main road (nearly the only road) and some minimal tourist infrastructure. Several dive shops, not as many hotels as you'd expect and a handful of restaurants. If you visit during the festival, the entire town is a restaurant. Most every resident seems to have set up a tent in their yard or on the street and is selling some sort of food, mostly fried things.
The large building on the left side in this picture is the historic Customs House. It doubles as an unofficial craft market as well. You can tour it during very sporadic opening times. This is a good idea if you are really interested in cannonballs.
The last couple pictures (and this one) were taken from Fort San Jeronimo which is the fort in the center of town. Visiting the forts of Portobelo is free and there is minimal information available on them at the forts themselves. The small white and orange colored cupola in this picture is the town cathedral. Normally you could visit and see the Black Christ namesake of the festival. Since everyone was in town to see it while we visited, we skipped it.
Yes, there is nothing really in this picture. This is typical of everything else around Portobelo. Inland, it is surrounded by thick jungle and national park areas. The opposite side of the bay can be visited by boat from Portobelo (it's not hard to find one) and the head of the bay is mostly mangrove swamp. There are supposedly lovely beaches accessible by boat (outside the harbor) but we skipped them given the weather.