Most activity on the state's largest construction project, the Minneapolis light rail line, is in plain view. But work on the most expensive part of the project is underground, out of sight.

The first sign of the monster boring the tunnel is a house-sized cone of sand piling up outside its huge burrow underneath Minneapolis St. Paul International Airport. Sand with the look and consistency of brown sugar falls off the end of a long, snake-like belt emerging from the tunnel.

"That's basically a continuous conveyer system up to the machine all the way out to here, and you see it piling up there where it's hauled away to various construction sites in the Twin Cities including LRT elsewhere," says Metropolitan Airports Commission tunnel project director Pat Mosites.

At least once a week Mosites enters the monster's lair to inspect progress on the $142 million project.

Fresh air gushes into the tunnel through a metal conduit along the ceiling. Wearing yellow hardhats, bright safety vests and calf-high rubber boots for slogging through sandstone muck Mosites leads us onto a wobbly metal catwalk for the one mile hike to visit the monster.

"If a train starts comin' we gotta lean on here," Mosites says, pointing to the tunnel wall.

We hitch a ride with a locomotive ferrying curved panels of concrete. The panels form the tunnel wall. Without them the sandstone would crumble and the tunnel would cave in. The five foot wide, six inch thick panels each weigh three tons. The forms are trucked in from a plant in Wisconsin where a French company makes them. Each panel, Mosites says, fits a specific length of tunnel.

"If it's a tight turn, or if it's diving down, or coming back up, so each piece is custom made in that sense but all the pieces fit like a jigsaw puzzle," he says.

We stop halfway, get off the train, clamber up a narrow metal ladder through sandstone to a huge cavern. When the Hiawatha line is complete this will be the Lindbergh terminal station.

"The whole cavern that you see in front of you which is like a mini-Metrodome is 525 feet long, 60 feet wide and 40 feet high," Mosites says.

Light rail passengers arriving at the Lindbergh station will ride escalators or elevators to the next level then ride another, smaller train, the people-mover to nearby Lindbergh terminal.

Finally, our destination. The behemoth.

Not a living thing in the organic sense; rather, it's a mechanical creature nourished with pressurized air and mega-doses of electrical power through a cable as thick as an arm.

The 300 foot long machine has just completed a meal chewing through a portion of sandstone. Each day the machine bores more than 100 feet of tunnel. It rests every five feet as workers clamber about the fresh section of tunnel. They move quickly to put the curved concrete panels in place.

A worker on a catwalk behind the machine's cutting blades gently works two joy sticks sending commands to a robotic arm. The arm grabs a three ton panel and lifts it into place. Another worker wields a huge pneumatic wrench to drive foot long bolts that secure the panels.

"They bolt them to the previous liner so it's cantilevered over. Once those are all in place the machine basically pushes off that newly installed section another five feet at the same time boring out the soil," Mosites says.

The behemoth's minder, literally the driver, is Dale Wiedrick. He watches video screens and control panels lined with rows of red and green lights. A laser beam pinpoints the next section of tunnel.

"The actual laser is on the top of the machine and it shoots over the top of the machine onto the heading where it has a target up there and what you see on the screen is like an airplane, going away from you and you keep the airplane heading toward the crosshairs on the target," Wiedrick says.

A bell sounds the warning for everyone to clear the area. The machine is ready to take its next bite. We retreat one mile to the tunnel mouth.

Fifty people work three shifts, around the clock, five days a week on the light rail tunnel project. The boring will be complete by late October.

By late 2004, officials say, the Hiawatha line will be finished, carrying passengers eleven and half miles, mostly above ground, from downtown Minneapolis, underneath the airport, then back above ground to the Mall of America.

Are we there yet? April 2002