When we have adjective with noun, an article can go with the adjective only (πχ η όμορφη γυναίκα), or both the adjective and the noun can take an article (πχ η όμορφη η γυναίκα).
The first case is more common. The latter is for more emphasis.
In this song the latter form is used, for a very practical reason: to have better rhythm.
"Μέσα στα στενά σου τα σοκάκια" means "Inside your narrow alleys". It is a line from the famous Greek folk song "Όμορφη Θεσσαλονίκη" written and composed by Vasilis Tsitsanis. Here is a link to the song: https://www.youtube.com/watch?v=T_wiz2b4bEg