This is the view down, below the platform. It's a concrete wedge, forcing the rocket exhaust into two tunnels that channel it out and then up, parallel to the silo, and eventually out into the atmosphere.
After the first stage ran out of fuel, it was jettisoned and the second stage, seen here, took over. It was less powerful, 100,000 pounds of thrust (445 kN), but burned for 15 percent longer, about 3 minutes. This pushed the Titan II to about 200 miles above the Earth.