I've been inspired by the guy who had pipes outside his house he didn't
know what they were there for!

In my basement (mid-70's construction) there are three places in the
basement floor that drain water flow into. Presumably they're all
joined somewhere under the basement and lead to the county sewer
system. In my house the pipes coming out of the concrete are cast iron
(or some kind of big thick black metal) for a foot or so above the
floor and the ABS plastic drain pipes are coupled on.

But in one place (roughly in the middle of the house near the chimney)
there's some other mysterious pipes coming up through the floor. They
look like cast iron to me. One is like an upside-down U, about a foot
high and two feet long, both ends going into the concrete. The other
looks like maybe is in there as a "future" drain, it's located pretty
much right under a vertical duct where maybe a drain stack might be put
in.

The house was originally built with an oil-burning furnace, but was
converted to electrical heating many years ago. Physically the oil tank
was located outside the house near the attached garage. I think the
original furnace was roughly where all three of these mystery pipes
were.

Any ideas? Maybe it's just conventional to put a drain near where the
furnace goes (for future dehumidifier?) What about that funny U-shape
pipe - maybe for protection, but why would you worry about physically
protecting the oil-burning furnace, it's not like there are forklifts
or delivery trucks driving around in the basement...