:salamext:
I dont think its a good idea to go to the cinemas because theres alot of freemixing like the brothers have said, and at the same time - a person is constantly staring at people from the opposite gender - without lowering their gaze.
Allaah subhanahu wa ta'aala says in the qur'an:
The Noble Qur'an - An-Nur 24:30
Tell the believing men to lower their gaze (from looking at forbidden things), and protect their private parts (from illegal sexual acts, etc.). That is purer for them. Verily, Allâh is All-Aware of what they do.
And tell the believing women to lower their gaze (from looking at forbidden things), and protect their private parts (from illegal sexual acts, etc.) and not to show off their adornment except only that which is apparent (like palms of hands or one eye or both eyes for necessity to see the way, or outer dress like veil, gloves, head-cover, apron, etc.), and to draw their veils all over Juyubihinna (i.e. their bodies, faces, necks and bosoms, etc.) and not to reveal their adornment except to their husbands, their fathers, their husband's fathers, their sons, their husband's sons, their brothers or their brother's sons, or their sister's sons, or their (Muslim) women (i.e. their sisters in Islâm), or the (female) slaves whom their right hands possess, or old male servants who lack vigour, or small children who have no sense of the shame of sex. And let them not stamp their feet so as to reveal what they hide of their adornment. And all of you beg Allâh to forgive you all, O believers, that you may be successful.
So if a person keeps staring at people from the opposite gender on purpose, it is a sin. And anything that leads upto a sin (even though it may be permissible) is also a sin, therefore its better you stay away from it insha Allaah.
Allaah Almighty knows best.
:wasalamex