Nobody is certain who made these unique and mysterious carvings or what became of the artisans and their civilization. I am not convinced they are all tomb markers and believe some may be far older than claimed by some modern archaeologists.
When I was visiting I was told the statues were between 1000 and 3000 years old! I noticed the Unesco site is now saying 100-900 CE. It seems like often archaeologists are changing dates, making things newer so they fit into the main stream historical narrative. There does not appear to be much evidence for the dating. They were rediscovered in the 18th century.
Many carvings I saw focused on anatomy. Pregnancy, diagrams of a human heart, a c-section birth, exaggerated facial features. Details like this led me to agree with my guide that all of the carvings may not be marking tombs. They could have different carvings for different purposes like ceremonial or to mark major events.
Some sites in the region did have carvings marking obvious tombs and their entrances. Sarcophagi were found as well.
The carvings would have been colorfully painted. Some less exposed ones still have traces of the color.
Whatever you believe about the date and use of these carvings they are quite unique. Many are in excellent condition and it is very easy to see the detail in the carvings.
The carvings can be easily visited on full and partial day excursions from San Agustin. It took us a few days to see most of them. The sites are spread over a large and very scenic area. Any visit to the sites will pass by some nice scenery, even waterfalls.
Even 11 years ago San Agustín was a comfortable town use to tourists. There was a range of lodging and restaurants. We did horse and van tours as well as some walking to the various sites. On the day long van the tour was in Spanish with some English. Most guides and tourists could speak some of both languages.
The statues are located in the south western Colombian Andes 9/10 hours by road from Bogota.
I took an overnight bus to San Agustín from Bogota and returned to Bogata by bus a couple days later. I took the regular public coach instead of the tourist bus which was a good choice. This was way back in 2009. I now avoid overnight transport where possible for comfort. These days it is hard for me to arrive early, unable to check into a hotel and spend a day sightseeing after a poor night of sleep. Local budget flights have come a long way in availability and lower costs. Hopefully there are better options now.
2020 update: These days bus tickets can be easily purchased https://www.redbus.co/en/bus-tickets/bogota-to-san-agustin
Tip: I always take the regular bus, not the tourist one that everyone in town tried to sell you tickets for. The overnight tourist bus from San Agustin was more cramped with less comfortable seats and was more expensive than the basic coach (I think it was Coomotor). This advice applies most places. I also feel you are less likely to be robbed on the regular bus than the tourist ones, which tend to be a target for pickpockets especially in heavily visited places like Thailand. Perhaps less of an issue these days with online ticketing, but something to keep in mind.