OFF the beaten path, in the north-centralregion of the country, TenorioVolcano rises over Arenal Lake, carpeted injungle and spilling rivers down its sides. Itis surrounded by 18,400 hectares of nationalpark land teeming with exotic plant life,rare birds andsome of CostaRica’s most excitingand rarelyglimpsed animals.Not on theradar for manytourists, TenorioNational Park is atreasure trove ofadventure andsights for visitorswilling to divergea little from theusual routes.Rising 1,916meters above sealevel, TenorioVolcano rewardsclimbers withpanoramic viewsreaching across the northern border toLake Nicaragua, sweeping over theGuatuso and San Carlos lowlands, andencompassing Lake Arenal and CañoNegro Wildlife Refuge.As Tenorio ascends, the vegetationevolves from savannah to rain forest atmid-elevation, and cloud forest at upperelevation. The volcano is not consideredactive, according to the Central AmericanSeismic Center at the University of CostaRica. Though legends mention ancienteruptions, no evidence of any exists inmodern history.ONE of the most renowned features ofthe park is the phenomenal Río Celeste, abrilliant lightblueriver coloredby sulfur and calciumcarbonatesin the water.H o w e v e r ,according to EliomarMuñoz,who works in thepark, if the wateris taken out of theriver, say, in aglass, it becomestransparent. Thecolor, he explained,is a visualeffect createdby the water,rocks in the riverand the sun – sothe stronger thesunlight, the brighter the blue of the water.The river actually begins clear, likeany other river, at the top of the volcano,and has the official name Río Buenavista,Muñoz explained. At a point known as ElTeñidero, Río Buenavista joins anotherriver, bringing the minerals together that cause the unique coloration and formingthe Río Celeste. The river continues 36kilometers from this point, plunging overa 70-foot waterfall and maintaining itsmilky-turquoise color the entire way.Trails lead in from various points,following the river past the waterfall toEl Teñidero. One well-known entrance isat Bijagua, one of the nearest communitiesto the northwest of the park. Anotherleads in from the small community ofNueva Guatemala, to the southeast of thevolcano, from where area guides willtake tourists to the top of the mountain,said Muñoz. He added that the hike tothe summit is strenuous and takes eighthours, and that the park service does notlike to encourage “that kind of tourism,because the ecosystem higher up isfragile.”But there is much to see in the parkbelow Tenorio’s peak. Stalking the forestsare pumas, margays and ocelots, aswell as tapirs and collared peccaries. Inthe canopy swing howler, white-facedand spider monkeys. Birdwatchers mightspot the three-wattled bellbird, turkeyvultures and different roadside hawksand tanagers, among many. Near the volcanoand Río Celeste are hot springs andthermal vents. In the southeastern cornerof the park is Cote Lake, which gainedfame after a government plane takingaerial photos of the lake and shoreallegedly captured a flying saucer.For accommodations near the park, LaCarolina Lodge (380-1656, www.lacarolinalodge.com) offers a place to stay,meals, trails leading into the park and tothe waterfall, and horseback riding. Therecommended time of year to visit is duringthe months of March and April, whenthe sun parts the incessant rain that fallsduring the rest of the year to keep this naturalgem green and healthy.