Seahorse in the Sky

This little-known story begins when more than a dozen people wake up in
coffins. They find themselves in a small area made to look like part of
a town -- it contains a fully stocked store and hotel, a car parked on
the street (that doesn't run) -- and a bunch of plastic coffins, each
containing a passenger from an international flight, each apparently
snatched out of midair, since there is no flight wreckage, and all of
them seem to be alive and unharmed.
The people slowly gather in the hotel and find themselves able to
understand one another perfectly, even though they don't all speak the
same language. None of them has any idea what they're doing in this new
place, and there isn't anything for miles around their little
settlement except a seemingly endless expanse of grass.
After several weeks of waiting for rescue that never arrives, a few
of their number explore and discover that this mysterious land is also
populated by a group of what appear to be medieval people and another
group of what seems to be cavemen. That accounts for the human
population on this island . . . the only other creatures around are the
sinister metal spiders.
This story is as much mystery as it is science fiction, because
these people must figure out how they got to this place, and why they
were chosen. But they also have to survive.