what is the meaning of "opportunistic houses" in this paragraph?
But this journey was extraordinary . . . it had a pioneer feel – the enormous Hudson,
with chunks of ice like broken pavement in the water;
and the huge wealthy forests, the valley full of forts and
power stations and opportunistic houses glooming on
vast icy bluffs, the railway stations more like adventurers’ huts than anything in Europe – barely manned
outposts without proper platforms, and with outlandish
names . . . Poughkeepsie, Yonkers, Schenectady; the train
high above the ground, the big wheels polishing the rails,
and the driver blowing that childishly dissonant horn.