、。
Even Takagi-san, who has lived here for 16 years, was surprised.
Literal
16-years, here [at-に] is-living Takagi-san [also-も] was-surprised.
A relative clause modifying a person, with the inclusive/focal も on 高木さん acting as 'even' rather than just 'also.' The も carries the implicit comparison: 'if even someone like Takagi-san, who has lived here for 16 years, was surprised, imagine everyone else.' Note that 住んでいる modifies the person via a relative clause, not via a separate sentence — Japanese doesn't need a relative pronoun, the clause just sits in front of the noun. The ~ている here is resultative/ongoing: Takagi-san has been living here (and still is) for 16 years.