There is a solution that can work if there is Verizon, ATT, Sprint, Etc., 4G in your area. The solution is not designed to stream movies or sound as this would cost a fortune. The application of using this type of service is for bringing internet access to a small group of users, or a single user.
You can visit Cradlepoint - www.cradlepoint.com and they have routers which can provide stand-alone 4G service where the actual router is also a Wifi radio. The IBR600 series -
This can provide a very nice signal and has a full-featured firewall built in. Configuration can be a bit tricky for the novice but someone with basic understandings of firewalls, wireless, and switching could configure the solution easily.
This would mostly be used in an office environment but the signal would travel a decent distance in the park. Of course, all the security features necessary are built in to a cradlepoint.
If you wanted to run something more complicated throughout the park, I would recommend Cisco Access Points.
I hope this helps.
Contact me if you have any questions.