Return Iobservable in a method

Question

I have a method that needs to return an Iobservable, but I’m having a lot of trouble. There is little content regarding this interface and what I find requires the use of the Reactive extension (https://docs.microsoft.com/en-us/previous-versions/dotnet/reactive-extensions/hh242985(v=vs.103)) Someone with knowledge regarding the Iobservable interface can confirm me if it is really only possible to return an Iobservable in a method with the use of that extension?

public class Graph<T> : IGraph<T>
{
    public Graph(IEnumerable<ILink<T>> links)
    {

    }

    public IObservable<IEnumerable<T>> RoutesBetween(T source, T target)
    {
        throw new NotImplementedException();
    }
}}