Woman going out on a mixed trip without a mahram

Mixing of a woman with men is haraam, and we have explained the evidence for that in the answer to question no. 1200. 

If this mixing is on a trip where people are more likely to be relaxed and start chatting, then it is more serious and harmful. Hence it is not permissible for a woman to go out on such trips, even if there is a mahram with her, so long as there is careless mixing; and her going without a mahram is more serious. Whoever agrees for his sister or daughter or wife to take part in such trips is lacking in protective jealousy and is weak in religious commitment. We ask Allaah to keep us safe and sound. 

And Allaah knows best.