Visited Tierradentro just recently (November, 2011). Visiting all 5 places (Segovia, El Duande, El Tablon, San Andres and Aguacate) requires at least full day on foot or riding a horse (although I am not completely sure about the latter possibility as the road are occasionally stopped by fence accessible by man only). All thirst four sites are protected and most of tombs are locked. They can be opened during visiting hours only (no additional cost except of entrance ticket). Aguacate is more remote (requires 500 meters climb and some 1,5 - 2 hours of mountain walking), very impessive (photo attached)