The visitors had come not to view the ruins, but to study and photograph dragonflies that have made it their habitat.
"Just a few minutes ago we found the ghost dragonfly which sit on the wonderful archeology you have," dragonfly watcher Mike Crotton says.
"But my favorite's are the tiny little gems that you get here that you don't get in the UK. Totally beautiful."
With niche markets like dragonfly watching growing in the West, specialized tour operators are now actively marketing dragonflies as a product to position Sri Lanka as one of the top dragonfly destinations in Asia.
The rich biodiversity, easy access to wildlife and a large number of endemic species of dragonflies have made Sri Lanka a good destination for dragonfly watchers.
"Dragonflies might seem a very unlikely market or product," Gehan de Silva Wijeyeratne, chief executive, Jetwing Eco Holidays says.
"But it is a growing market and we have 52 species that is not found anywhere else in the world.
"So the same things that make Sri Lanka good for bird watches also makes it good for dragonflies or mammals or anything."
De Silva Wijeyeratne, himself is a birdwatcher and wild life photographer, who has authored several books.
The group in Arankelle, were from the British Dragonfly Society.
"Annually we get this group here, through the British Dragonfly Society and we have been traveling around the country," says Chandraguptha Wickramasekara, a naturalist at Jetwing Eco Holidays,
Karen Coniff, an entomologist and a dragonfly lover says Arankelle, with its ancient ponds and intermediate climate provides an ideal habitat for a variety of dragonfly species in Sri Lanka.
"It's got a lot of water and pools and is a dry and intermediate mixed zone and so you get a mix of dragonflies and you usually see a few that you have not seen anywhere else."
Though butterfly and dragonfly watching are specialist niche markets in Europe, eco tour operators like Jetwing say Sri Lanka is well positioned to attract dragonfly watchers from Europe which can generate large volumes of revenue.
"Sri Lanka has in the last couple of years three specialist dragonfly groups coming in here, with the express intent of watching and photographing dragonflies," Gehan Says.
"We have also other clients and we have field guides which make it possible, so it is a growing market and is worth serious money."
De Silva Wijeratne says if ten tour operators could bring in specialist groups to watch dragonflies the industry could earn a profit of10 million rupees.
But the potential for revenue generation for the tourism industry will depend on the conservation of dragonfly habitats, especially rain forests.
British wildlife lovers say Sri Lanka should develop the economy, while protecting its environment.
"While still growing your economy you must protect your environment," says Crotton.
"So many of us in the West, have made the mistake of growing the economy and forgetting to protect the environment."