To behind, to under

Question

I can be behind the house and throw stones:

I am throwing stones behind the house

If I am in front of the house and throwi the stones onto the territory which is behind the house, I should say something like:

I am throwing the stones to behind the house

But it seems to be wrong

Once I had a similar question with there and to there

I was asking about

You go there or only to there

And some good person told me there was a word "thither" which was archaic but it suited perfectly. Is there any archaic word for "to behind"

Because the same problem happens with "under"

The car is going under the bridge

Where is the car?

It's on its way to under the bridge

OR

It's already under the bridge and is going somewhither?

Answer 1

I recall this post of yours where similar questions were brought up. As I may have mentioned there, to + (other preposition) generally sounds unnatural. Usually the meaning you want to convey is understood if you omit the to and just use the other preposition:

I am throwing the stones behind the house.

The car is headed under the bridge.

If you want to use to you should opt for a noun phrase rather than another preposition:

I am throwing the stones to the back of the house.

The car is headed to the place under the bridge.

Answer 2

If you were indeed throwing stones to the back of the house, you would presumably be throwing stones _over_ the house, but more likely you mean round the side which might be throwing stones _past_ the house or more likely throwing stones into the back garden.

The car is going under the bridge - fine.

The (car) is on its way to the bridge - no need for under.

It's already under the bridge, and on its way - I've heard of hither but not somewhither, certainly not common/natural.