I think in general high-elevation terrain other than mountains is underutilized. Other features: atolls with their lagoons and coral island cays; tidal islands constantly submerging and reappearing, or sparsely-inhabited rocky skerries; peat bogs such as Carbajal Valley, a living, primordial ooze of a landscape; or their predecessor, Everglades-like carrs, with mangrove marshes similar in a different context; the kettle-dotted lands of 10,000 lakes of America's middle north, including the Boundary Waters; the Amazon-flooded Varzea [forward accent on the 'a'] forests, or similarly, Igapos [forward accent on the 'I']; muskegs often look pretty interesting https://www.reddit.com/r/pics/comments/74mrsf/muskeg_forest_island_canada/ & https://sierraclub.bc.ca/more-muskeg-the-taiga-plains/ ; the pillared cliff landscapes of Zhangjiajie National Park; fog oases or fog-watered 'Lomas' - very cool; high-altitude temperate rainforests such as the Pacific Northwest ... hopefully these give you some ideas :)
