BOB THOMAS, a Philadelphia architect who has devoted his life to preserving historic buildings and planning greenway trails, chills out yesterday by hiking in Fairmount Park - to what he calls a "secret treasure" that he wishes wasn't a secret.

Starting at the Shofuso Japanese House and Garden, Thomas hikes an unmarked trail that rises along the steep wooded banks of Lansdowne Glen creek.

The trail leads to artist Martin Puryear's "Pavilion in the Trees," a wooden deck under a latticed canopy that juts out 24 feet above creek and glen, offering a spectacular view.

The only sounds are the chickadees, wrens and sparrows in the towering trees and the melting ice falling off branches and hitting the slushy ground.

The only tracks on the snowy trail are made by deer.

"We are the only humanoids here, but we shouldn't be," says Thomas, 66, who has devoted decades of his days off to leading Philadelphia Parks Alliance hikes through the wild beauty of city parklands.

Thomas points to Memorial Hall, visible through the trees.

"You should be able to walk out of Memorial Hall and take the trail here," Thomas says. "But there's no signage, so nobody knows about this. There are too many incredible Fairmount Park trails that have no signs, so people don't know they exist."

As a founding partner of Campbell Thomas & Co. Architects who has been deeply involved in the Fairmount Park Bikeway and Rail Trail, and the Philadelphia-Valley Forge Bikeway, this frustrates Thomas.

The activist architect vows to lobby the city's Parks & Recreation Department to put up Pavilion in the Trees trail signs.

Then he heads up another unmarked trail, where he and the deer know the secrets of Fairmount Park's hidden jewels, and he is anxious to share them with the public.

- Dan Geringer

Chillin' Wit' is a regular feature of the Daily News that spotlights a name in the news away from the job.