Domain pointing to a subfolder

Hello from Madrid. I’ve read hundred, if not thousands of posts and pages. Many of them “talk about the same issue”, but I coudn’t solve my problem yet.

I have two sites:
12.34.56.78 (as “primary site”)
12.34.56.78/othersite

My domain xxxxxx.es currently points to 12.34.56.78

I want that my domain xxxxxx.es point or adress to 12.34.56.78/othersite.

I’ve tried to install MU Mapping Domain, but I coudn’t (lot of problems with SUNRISE, domain mapping…)

Some people say that I should modify my .htaccess, but I’m not sure.

Any ideas? Thank you!