。
By this time tomorrow, I'll be sightseeing in Osaka.
Literal
Tomorrow [possessive-の] this-about-time [topic-は] Osaka [object-を] be-sightseeing probably.
今頃 ('this-about-time / around now') used with 明日の produces 'around this time tomorrow' — a common way to project a current-time-of-day onto a future date. The ~ている form on 見物する marks the action as ongoing at that future moment, not just 'will sightsee.' 見物 takes を for the thing being sightseen. A future-progressive construction.