Question 1

Where is Observation Mountain shaped like an ancient burial mound?

Accepted Answer

Observation Mountain shaped like an ancient burial mound is in Inzai, Chiba, Japan. You can see its exact position from the map coordinates and the Street View link.

Question 2

Which scene of Wonder Egg Priority does Observation Mountain shaped like an ancient burial mound appear in?

Accepted Answer

Observation Mountain shaped like an ancient burial mound appears in OP of Wonder Egg Priority.

Question 3

Can I visit Observation Mountain shaped like an ancient burial mound?

Accepted Answer

Yes. Observation Mountain shaped like an ancient burial mound is a real place you can visit. Check what it looks like on Street View before you go.

Question 4

Where was Wonder Egg Priority filmed?

Accepted Answer

Anime and manga are not filmed the way live action is. Their backgrounds are painted from photographs of real locations, and Observation Mountain shaped like an ancient burial mound is one of those real places (OP).