An unhandled exception of type 'System.StackOverflowException' occurred - using Cache'd class

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C#

.NET

.NET4

cache

I have a class as in the following:

public class activityDetail
{
  public string a { get; set; }
  public string b { get; set; }
}

then what I want to do is define a singlton class in my Cache.cs as in the following:

public sealed class Cache
{
private static  readonly Cache cacheInstance = new Cache();
.
.
.
.
public activityDetail instanceofActivitydetail { get { return instanceofActivitydetail; } }

Now, in my controller I want to reference this instanceofActivitydetail, if I do it the following way I get an exception (some type of stack overflow):

Cache.CacheInstance.instanceofActivitydetail.a = some value; 
Cache.CacheInstance.instanceofActivitydetail.b = some other value;

// "some value" is just for ease it actually have a designated known value but it is not easy to share it here.
// so when the compiler eaches this line it throws the error mentioned above, I believe my defninition in the Cache class is missing something, or my call shown above from the controller is missing something.