Where do strings 'exist' ?

[S = k log w]

Pardon me. I claim ignorance. Where do strings 'exist'? Either? 'String Space'? If so, is there space between on string and the next? What, if anything 'fills' the 'void'(s)? How can strings be fundamental if they have to lay in (some) dimension(s)? Do strings define themselves? If not, what defines strings?

[Ambitwistor]

In perturbative string theory, strings exist in ordinary space, just like particles. Some people would like to derive space from string theory, in a non-perturbative, background-independent way, but it is not yet clear how this can be done.