This is an interesting one, because the vagina can seem like a mysterious place 0_0 Let's see if we can demystify it!
First, our wonderful founder has a lengthy article all about the vulva and its many parts: Innies & Outies: The Vagina, Clitoris, Uterus and More
It sounds like you discovered new depths by using the circling motion to kind of 'open up' more. The vagina is stretchy, so being able to 'open up' like this shouldn't be difficult. I would guess (but can't confirm, since you know your body better than any of us here) that you might have been able to push past the pubic bone to access the full length of the tube.
Re: pain and penetration, it can
hurt, but it doesn't have to. The friction between body parts can certainly feel strange or painful, especially if you aren't aroused and/or unlubricated. The vagina at rest (as in, when you're not aroused) may feel like it's unable to accommodate certain lengths and volumes compared to when you're aroused and 'wet.'
Does all that make sense?