"a ribbon of sand between the angry sea and the placid bay"
"the quiet waters of a lagoon"
"a lake of tranquil blue water reflecting a tranquil blue sky"
"a smooth channel crossing"
"scarcely a ripple on the still water"
"unruffled water"
"spoke in a calm voice"
"remained calm throughout the uproar"
"he remained serene in the midst of turbulence"
"a serene expression on her face"
"she became more tranquil"
"tranquil life in the country"