Ranikhet is a place of remarkably _____ beauty.

The blank requires an adjective to modify 'beauty', preceded by the adverb 'remarkably'. 'Scenic' is an adjective meaning providing or relating to views of impressive natural scenery, which appropriately modifies 'beauty'. 'Scenery' and 'scene' are nouns. 'Scenically' is an adverb. The structure 'remarkably + adjective + noun' requires 'scenic' to fit grammatically. Hence, 'scenic' is correct.