Surrounded by ruins and ancient mausoleums, the Laguna de los Condores was wrapped in clouds and crowned with a rainbow when we arrived. Our group had made the grueling trip to this mountain lake at 7,200 feet elevation in hopes of uncovering a secret. The lake is in the northern Peruvian Andes near an area once inhabited by the pre-Columbian Chachapoyas culture. These fierce warriors were the last defeated by the Incas. In 1996, archeologists discovered more than 200 Chachapoyas mummies in a mausoleum constructed into a steep cliff high above the lake. Protected by a huge overhanging rock and hidden behind a small waterfall, this secluded burial ground had preserved the dead so well that they withstood the permanent humidity of the Peruvian cloud forest for more than 800 years. The expedition's goal was to study the aquatic biodiversity and the sub-aquatic archeological potential of the Laguna de los Condores. The scientific group Mundo Azul organized the project with the Peruvian National Institute of Culture and the German Association for the Support of Underwater Archeology. Our team left Peru's capital, Lima, and headed north along the coast to Chiclayo and then east into the Andes. After three days of driving on dusty dirt roads, crossing rivers over virtually impassable bridges and moving aside broken-down cars, our group reached the little community of Leymebamba. Here we packed 1,200 pounds of scientific instruments, laptop computers, diving equipment, gasoline, food and personal belongings onto mules and started off on the last leg of our journey. For 12 hours, our caravan of 43 mules and horses and 26 local guides crossed more small rivers, waded through knee-deep mud and climbed over rocks to reach the lake. The next two days were spent measuring depths in the lake with echolocation devices and building a floating platform of bamboo and truck tires. We did not see a single ray of sunshine during these days and the unusually heavy rain in the middle of the dry season concerned our local coordinator, Wilton. "The guides are afraid and want to return," Wilton whispered to me. "The lagoon doesn't want us to be here." Wilton said there was only one way to pacify the lagoon's spirits: an offering. The rain was coming down harder than ever when our group gathered on the lake's shore the next morning. Our tongues slowly became numb as we chewed coca leaves and spit the holy alcohol into the air while listening to Wilton's prayers. Most of us had followed the procedure with scientific skepticism. But the rain stopped 10 minutes later and a clear blue sky emerged, remaining for the rest of our time at the lake. It's hard to argue with success. The underwater conditions proved to be another surprise. The visibility was at least 45 feet, but divers would quickly be swallowed by darkness without their lamps. Humic acids produced by decomposing organic matter left the water tinged reddish brown, making it seem like we were diving in a huge cup of tea. The dark water limited plant life to the top 20 feet of the lake. Huge fallen trees on the muddy bottom provided hiding places for plenty of fish. After diving the lake's northern shore, we were even more curious about what we would find to the south, where a huge cliff edged the lake. We knew from our echolocation that the wall continued straight down for 150 feet before angling off at 45 degrees to the lake's center. We discovered massive submerged overhangs jutting out from the wall, and huge cracks that beckoned for exploration. For days we collected biological samples and searched for archeological remains. In the sediment of a nearby river, we saw indications of man-made construction that was possibly intended to secure the shoreline or change the river's flow. Although we didn't find the lost gold of the Incas that legend says is in one of these Andean lakes, the group came away with unforgettable memories. There were even times we thought we could hear the ghosts of the cloud warriors whispering in the rain drops. One thing is for sure: We will return. Stefan Austermuhl is director of projects and scientific investigation for Mundo Azul. For more about this story, visit www.peru.com/mundoazul.