。
She took a round-the-world trip last year.
Literal
She [topic-は] last-year world-circuit-trip [object-を] did.
世界一周 ('one circuit of the world') is a fixed compound built from 世界 (world), 一 (one), and 周 (circuit/round) — the same 周 appears in 周辺 (surroundings) and 周回 (lap, orbit). 旅行をする ('do a trip') is a light-verb construction: many Sino-Japanese activity nouns pair with する (or をする) to form a verb. The same template gives 日本一周 ('a trip around all of Japan'), a culturally weighty bucket-list goal often pursued by motorcycle, bicycle, or even on foot.