Oh, just inside that central soffit thing is one monster steel I-beam. Sure, there are I-beams running the length of the basement, but that particular one is holding up a 25' clear span (no intermediate posts). So it is rather thick and extremely heavy.

That mongo I-beam was responsible for a nearly 3-week pause in construction of the home, as two flatbed trucks broke down trying to transport it to the site. With a ripple on effect that those weeks were nice dry weather, and the month that followed was more or less continuously rainy. The roof didn't get closed in until the day after the rain finally stopped.

The yellow thing running crosswise to it, up among the floor joists, is a pair of quite beefy LVL beams, which are carrying much of the load of a stone wall and wood stove on the level above the workshop.