The Subjects API serves to get information related to a specific subject, primarily related works.
For more usage examples of this API, see MiscellaneousExamples.
To get a subject's related data, use the OpenLibraryClient
OpenLibraryClient client = new OpenLibraryClient();
var parameters = new List<KeyValuePair<string,string>>() { ... };
OLSubjectData subjectData = await client.Subject.GetDataAsync("fantasy", parameters);
or the static OLSubjectLoader class:
HttpClient httpClient = new HttpClient();
OLSubjectData subjectData = await OLSubjectLoader.GetDataAsync(httpClient, "fantasy", parameters);
For valid parameters, see the link above. Alternatively, see OpenLibraryUtility's Maps.