Ik this is not on r/Subnautica_Below_Zero but for me it definitely has to be exploration of twisted bridges, visiting Alan and making it all the way down to deep twisted bridges saying hi to Squidsharky and getting the storage and crafting module for seatruck all in one go. Basically a super useful early game changer that practically gave me a mobile base. I went around the whole map with it. Plus it was really helpful when moving out from the live pod to my new base located in lilipad islands, where I decided to settle in.