noun
travel diary; travel journal
A diary or journal kept while traveling, recording experiences, observations, and reflections.
彼は旅日記をつけながら日本中を歩いた。
He walked all over Japan while keeping a travel diary.
祖母の若い頃の旅日記を見つけた。
I found my grandmother's travel diary from when she was young.
旅行記 is a travelogue or travel account, often more formal or published, whereas 旅日記 is a personal diary.
Compound of 旅 (tabi, 'travel') and 日記 (nikki, 'diary'). The reading にっき is a standard rendaku-influenced form of 日記.