ATV riding.
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There is an attractive colonial-era building in the nearby town of Salgar, about 20km out of town. It is located on a cliff overlooking the sea and unlike many of the nearby beach resorts is free. It's a peaceful escape from the city if you are looking for some fresh air. The road along the coast is a pleasant cycle ride from town with only one big hill.
Archaeological museum of the Karib Peoples.
Classic bowling place.
It is possible to get to the end of the breakwater that helps manage the flow of the Río Magdalena out to the Caribbean Sea. There is sealed road from the city to Las Flores district, then gravel road (Calle 106) to a small settlement with some restaurants and beaches. After that it is a very bumpy path that gradually just becomes a scramble across the rocks. It is possible to cycle most of the way up the path, or get a lift on a motorcycle or with a horse and cart, but you will need to hike the last kilometre or so. There are informal settlements all the way along the route, and some of the local fishermen sell drinks and snacks along the way. Make sure to bring plenty of water and sunscreen. Note that this is not the safest place in Barranquilla. Theft and robbery at knifepoint have been known to occur around the site. Go only during the daytime if you choose to go at all, and take appropriate care; police do not have much presence here. Many residents of Barranquilla avoid Bocas de Ceniza and advise tourists to do the same.
Park along the water's edge. Restaurants, playground, and a good place to stroll and take in the sights. Stretches from Calle 80 down to Calle 72, and extends even further south as a cycle path. There are a few small restaurants and food stalls, but most of the stretch is underdeveloped and very quiet. It's windy and peaceful. In the southern area, when the wind hits the riverbanks at a certain angle, it plays musical notes, like an organ.