Sept. 23 (Bloomberg) -- Inside the sober exterior of the California Academy of Sciences, an elevator plunges through four stories of rain forest into a glass-tunnel swamp alive with wriggling armored catfish and spotted peacock bass. It's the most fun you could have while being hectored to save the planet.

The academy opens its sparkling new building in San Francisco's Golden Gate Park on Sept. 27, replacing a complex severely damaged in a 1989 earthquake. It's a research institution, but to the public it is an occasionally unwieldy combination of the Kimball Natural History Museum, Steinhart Aquarium and Morrison Planetarium. Every penny of its hefty $488 million cost is on view, gorgeously packaged by the Italian architect Renzo Piano.

Its overarching messages are the essential role of evolution in the work of the natural sciences and the urgency of addressing global climate change. In Piano's design, the medium is the message.

Piano has said he didn't want the usual black-box ``kingdom of darkness'' found in many natural-history museums. Working with the local branch of Stantec Architecture and the London-based engineering firm Arup, Piano eliminates a great number of energy- sucking lights by suffusing the 410,000- square-foot building with daylight, not least in heavenly bands emitted by round skylights poked into the roof.

Welcoming Porch

Thin, narrow sheets of translucent glass (banded with power- generating photovoltaic cells) project from the roof to form a welcoming, shadow-striped porch. Along with a lobby, Piano offers a light-filled outdoor central courtyard, roofed by a marvelous contraption of draping cables and pipe braces. It supports a partial glass roof as well as layers of shades that can adjust the courtyard's acoustics, cut the sun and keep out the rain.

The light in the court is as pleasing and ethereal as a trellised arbor on a languid afternoon. Yet the magical reflections of the cable structure on the glass surrounding the court compete with the vistas beyond.

On one side, a sphere wraps the planetarium. On the other, a tropical forest grows within a matching 90-foot-diameter glass globe. Burbling on all sides are the tops of aquarium tanks. They're home to some 32,000 aquatic plants and animals, with habitats ranging from the California coast to a Southern swamp populated with alligators. The underside of the planetarium is chopped at a dramatic angle to maximize the sunlight for a Philippine coral-reef tank.

Square Peg From Outer Space

The planetarium is the square cosmic peg not fully reconciled with the round hole of the museum's ecological vision. The 30-minute ``Fragile Planet'' program uses advanced computer graphics to illustrate the dangerous scope of global warming on Earth, yet it's not quite up to the task, lacking crispness and color. The show inevitably takes us into the stars -- looking for signs of life -- because that's what planetariums do.

A spiraling ramp ascends within the rain forest's greenhouse sphere. It begins in a sunken forest where you peer down through waters alive with fish. You amble through what is growing to become a shadowy understory, home to orchids and butterflies. The ramp emerges into the misty treetops, favored by brightly colored birds busily shredding fabric tree supports for nesting material.

As in the courtyard, Piano unleashes his hardware fetish in the rain-forest globe: glinting fasteners, crisscrossing cables and braces -- all as elegantly purposeful as yacht rigging. In its World's Fair gee-whiz, this fretwork is part of the fun.

An elevator atop the globe plunges through the rain-forest waterline to the dim labyrinth and 38,000 creatures of the Steinhart Aquarium. A 25-foot-high coral reef, swarming with brightly flashing fish, dwarfs jaw-dropping visitors.

Natural Ventilation

Piano bookends the main floor with high spaces enclosed by shaded, full-height window-walls. They automatically open and close to ventilate the entire main floor, demonstrating the Bay Area's richest source of alternative energy: its mild breezes. The elegant architecture upstages surprisingly dull exhibits on climate change and the roots of evolution.

Take the elevator to the roof, where the spheres below seem to have pushed the roof into hillocks greened with 1.7 million flowering succulent plants. It's part of the lesson plan -- the green roof sucks up rain, keeps water out of the overburdened sewage system and provides insulation.

Opening to city and bay vistas, it couldn't be more delightful, nor more poignantly remind us of our roles as stewards of a stressed planet.

(James S. Russell is Bloomberg's U.S. architecture critic. The opinions expressed are his own.)

To contact the writer on the story: James S. Russell in New York at jamesrussell@earthlink.net.

Last Updated: September 23, 2008 00:01 EDT