In order to create a social in a different city you simply need to change your location to that city from the top of the page, then create your social.
You can create a social in as many cities as you wish by using the duplicate social tool - again all you need to do is just remember to change the location beforehand from the top box.
Keep in mind that those socials will only be visible in the city you created them in, which means that when you go back to your own city you will not see them in the social list.
If you are planning a trip to a different city and would like people from your own city to join, you will need to post the social in your city, explain the trip in the title and description and use the location of the train/bus station as the venue.
For more information on creating social please see the following article on how to create a social.