Santa Marta is a city in Colombia.
Northeast towards Riohacha
Walk out towards the fork in the road at a newly constructed roundabout, and traffic lights (3 km or so) on Calle 29. Cars can be flagged from here, though this took time.
It may be better to hop on a bus headed to Bonda, a local service, and get off when it takes a right fork in the road, 5km out of town. There are speed bumps around this area.
The main road enters from the north area of town, so if you are headed north, you can avoid entering the city.
Other useful info
If you area heading to Tayrona NP, it is quite easy to sneak in to this NP. Alternatively, continue about 5km further north from the entrance, and there is a beach access road, which leads to a beach where wild camping is wonderful and easy, on a stunning beach. Playa Los Angeles. Quite easy to get out of a 10,000 Peso access fee they try to charge.