I believe you are looking for the Place Details endpoint for the Places API Web Service.
Hit the endpoint like so:
https://maps.googleapis.com/maps/api/place/details/output?parameters
Parameters will be a string containing your access key, PlaceID, and (optionally) the desired response data type.
The output will be either json or XML, according to what you specify in your parameters. In the response there should be an array in the result object called 'reviews'.
Display and use the reviews as you would any other array of data you need in your application.
The documentation for this endpoint, linked above, is very helpful. If you need to locate the ID of a particular place in order to use the above endpoint, check out Place Search Endpoint.