/usr/include/geos/util/ is in libgeos++-dev 3.5.0-1ubuntu2.
This file is owned by root:root, with mode 0o755.
..
/usr/include/geos/util/Assert.h
/usr/include/geos/util/AssertionFailedException.h
/usr/include/geos/util/CoordinateArrayFilter.h
/usr/include/geos/util/GEOSException.h
/usr/include/geos/util/GeometricShapeFactory.h
/usr/include/geos/util/IllegalArgumentException.h
/usr/include/geos/util/IllegalStateException.h
/usr/include/geos/util/Interrupt.h
/usr/include/geos/util/Machine.h
/usr/include/geos/util/TopologyException.h
/usr/include/geos/util/UniqueCoordinateArrayFilter.h
/usr/include/geos/util/UnsupportedOperationException.h
/usr/include/geos/util/math.h