Let X(t), t ∈ T be a centered Gaussian random field with variance function σ 2 (·) that attains its maximum at the unique point t 0 ∈ T , and let M (T ) := sup t∈T X(t). For T a compact subset of R, the current literature explains the asymptotic tail behaviour of M (T ) under some regularity conditions including that 1 − σ(t) has a polynomial decrease to 0 as t → t 0 . In this contribution we consider more general case that 1 − σ(t) is regularly varying at t 0 . We extend our analysis to random fields defined on some compact T ⊂ R 2 , deriving the exact tail asymptotics of M (T ) for the class of Gaussian random fields with variance and correlation functions being regularly varying at t 0 . A crucial novel element is the analysis of families of Gaussian random fields that do not possess locally additive dependence structures, which leads to qualitatively new types of asymptotics.