Does anyone know of some real world cultures, with practises, traditions and beliefs that could be utilized in a story? I'm trying to build a non cliche merfolk civalization. One which would make children raised by them see the land as very forgein and alien.
Really depends on which way you want to take the story. From what I have seen (sea-n? most depictions of merfolk lean heavily on the hunter-gatherer angle, and for some reason the merfolk are always temperamental and territorial. There are thousands of cultures to choose from so probably best for you to look at what your thoughts are already about the culture (as it fits the storyline) and work your way backwards.
You may want to look into conworlding, and, less directly, conlanging; there are people that spend a lot of their free time making up made-up cultures and languages (myself included), and there are a few forums online for those kinds of people. It might behoove you to get into conworlding a bit if you're dedicated to this story, because it'd help you create a more believable culture rather than just ripping off an entire culture from earth.
Maybe you could draw inspiration from Vikings. They had this intense love for the sea and were out in their massive ships for most of the year.
Viking, Orcadian, Shetlander, St Kilda etc all are interlinked but are based on the sea and life around it.
