、、。
What at first glance seems perfectly ordinary is, in fact, actually difficult.
Literal
This one-look, obvious [like-のように] look [nominalizer-こと] [subject-が], in-truth difficult [explanation-のである].
A thesis-statement-style sentence. 一見 ('at first glance') is a formal Sino-Japanese adverb. あたりまえ ('obvious, natural, expected') is common everyday vocabulary here set up in formal register. のように見える ('looks like / seems like') is the standard 'appears to be' construction. 実は ('in fact, actually') introduces the reveal. のである is the formal written copula — a literary version of のだ, often found in essays and editorial prose. The whole sentence captures a reflective 'what seems simple is actually hard' thesis.