If you liked the Boku wa Beatles manga, the Anime-Planet community thinks you'd like:
On the way home from a business trip, 48-year-old Hiroshi Nakahara boards the wrong train and finds himself in the town of his youth. After visiting his mother’s grave, Hiroshi is transported back in time to his fourteen-year-old self – a time when his family was strong and his father hadn’t abandoned them yet. At first he’s thrilled, but soon comes to realize that he isn’t able to return to his wife and children, and must continue living in the past. However, Hiroshi is now left with a life-changing decision – should be try to change the past, without knowing what it will do to his future?
Both are seinen manga where the protagonists suddenly find themselves in the 60s. Since they retain all their life experience and knowledge of what is now the future, getting ahead and taking advantage of thier situation is almost too easy. But what are the consequences of altering the past, and is it worth it?
In ancient Rome, renowned architect Lucius is down on his luck. He has been fired because his style of buildings is unfashionable, and all the bathhouses in the city are noisy, boisterous places that no longer prioritize relaxation. To get some peace and quiet, he sinks below the surface of the water, the only place where his fellow bathers' chatter can't reach him, but a powerful drain pulls him into the depths! Upon emerging, he finds himself in a vastly different bathhouse, and though the architect believes it's just the slaves' quarter, he's actually been pulled through time to modern-day Japan! Now, armed with knowledge of these strange new baths, Lucius is determined to restore his reputation and revolutionize the Roman bathing culture!
These two time-traveling seinen manga take the most ridiculous concepts and make them work fabulously. If you liked the historical quirkiness in one, you should appreciate it in the other (though Thermae Romae is much more comedic). The art style is fairly similar as well.