OPEN QUESTION: How "Small" can We Probe, In Distance?

WHAT is the smallest length humanity can currently probe?

I know that the smallest order of magnitude we can proble, timewise, is on the order of attoseconds, being defined as follows:

An attosecond is 10^-18, a billionth of a billionth, of a second. An attosecond is to a second as a second is to the age of the universe. In three attoseconds, a beam of light traveling 300,000 kilometers per second can get only from one side of a water molecule to the other. And the electron of a hydrogen atom, dissolved in a hazy cloud of quantum mechanics probability, sloshes from one side of the atom to the other every 24 attoseconds — a fundamental oscillation dubbed the atomic unit of time.

From:  here.

But that's not my question. My question is how deep down can we can dig in SPACE, in LENGTH that is.

It was pretty easy for me, using Google,  to discover how fast we've probed, but finding a LENGTH has been surprisingly difficult, so I'm throwing the question out to the community.


HELP!