Location of carotid sinus is:
Carotid sinus:

It is a fusiform dilatation at the terminal end of common carotid artery or at the beginning of internal carotid artery. 
It has rich innervation from glossopharyngeal, vagus, and sympathetic nerves. 
The carotid sinus acts as a baroreceptor (pressure receptor) and regulates the blood pressure in the cerebral arteries.

Key Concept:
Carotid sinus is a fusiform dilatation at the terminal end of common carotid artery or at the beginning of internal carotid artery.
At the termination of CCA
Behind the bifurcation of CCA
At the beginning of ICA
Both 1 and 3