I’m considering booking the Dark Cave tour in Phong Nha but honestly a bit hesitant about the mud bath component. How messy does it actually get and are there facilities to clean up afterward? I don’t mind getting dirty for a good experience but want to know what I’m signing up for. Are there other activities included in the tour besides the mud bath, or is that the main attraction? My girlfriend is excited about it but I’m more interested in the cave exploration aspects. Can you skip the mud bath and just do the cave tour, or is it all packaged together? Also wondering about what to wear and whether we need to bring changes of clothes. Any recent experiences with the tour that can give me a realistic idea of what to expect would help me decide whether to book it.
read about the dark cave tour here first before going. this guide got most of the questions you asked covered.
yes. there is kayaking and water sports including phong nha zipline just before you enter dark cave.
ofcourse you can but my question is why do you want to skip the mud bath because personally for me mud bath was the best part of dark cave after zipline lol
you gotta bring a swimsuit for you and your girlfriend. and bring a towel maybe with an extra pair of dry clothes. although you don’t really need the extra pair of clothes but I assume you might do the botanic garden tour next where you are definitely going to get wet either from sweating or maybe a jump in the waterfall 
just go. its one of the most fun part of phong nha tbh. don’t overthink it.
and combine another cave like paradise cave or maybe mooc spring/botanic garden on the same day with dark cave. because why not!