If your boss absolutely forbids you from going on a trip, this is an example of an insuperable obstacle to you going on the trip.
Origin of insuperableMiddle English from Classical Latin insuperabilis
Origin of insuperableMiddle English from Old French from Latin īnsuperābilis in- not ; see in- 1. superābilis superable ; see superable .
(comparative more insuperable, superlative most insuperable)
From Latin insuperabilis