1.   His eyes were like bottomless brown pools.

2.   His eyes, dark as bottomless pools, were hard to read, but held more than a trace of cynicism.

3.   His bottomless pool of personal charisma might as well be empty, and his high-flying public approval ratings are proving to be cold comfort.

4.   Rather, they evidently relished the opportunity to conduct unrestrained research on a bottomless pool of subjects.