It's very easy my friend I have hosted a lot of events here just on the beach. Usually I create a website to let everyone know about it (but we don't release the location until 24 hours before hand). I have a team I work with and we promote it on Instagram (I am not a fan of social media either but some times we have to accept it).
It's great that you know DJs, usually I just rent a speaker, find the location (you mentioned something similar to a cave in your city?) Take them all down there at the event time and release it via the website. Have a go making one and send it here when it is ready, also let me know when it is! You could make it Orchid themed!!
