Help! crawl space question

[seaglass]

We bought a house almost 5 years ago for our retirement which we are planning to move into within the next month.

The original owner added two additions, one on each end of the house, with no access to the crawl space.

I have been dealing with the fact that this allows mice in our attic and cellar (I'm not sure what to call this as the cellar does not go under the whole house). I am really squeamish about critters so please don't say anything about mice being on our main living floor.

So, this week I guess some animal got into the crawl space and died. But I really can't live like this so I either want to sell the house or find out what is needed to make the crawl space accessible or fill it in with cement or whatever will prevent animals from getting into this space and therefore the house.

Does anyone know what this would entail?

Thanks!