Practical English Usage by Swan or English Grammar in Use by Murphy have complete explanations. Here is the basic usage. "The" is not used before most proper nouns. Germany, not the Germany. "The" is used before most multiword proper nouns that include a common noun (or an implied common noun). The United States The United Kingdom The Atlantic (Ocean) The Sahara (Desert) The Eiffel Tower "The" is not used before proper nouns that include a person's name or a place before a common noun (or an implied common noun). Buckingham Palace Manchester Airport Presumably Tokyo Tower is in this category. There are exceptions and there are differences between British English, American English, Australian English, .... Like DavidK, I would say "the" Tokyo Tower. More information here: https://www.ef.com/ca/english-resources/english-grammar/definite-article/ [excerpt] Use "the" with the names of famous buildings, works of art, museums, or monuments. EXAMPLES Have you been to the Vietnam Memorial? We went to the Louvre and saw the Mona Lisa. I would like to visit the Eiffel Tower. I saw King Lear at the Globe.

in the US, our well-known skyscrapers (buildings, towers etc) are labeled with "the". Parks, stadiums, etc typically aren't. English translations of foreign names might follow a different convention, but to my ear 'Let's go to Tokyo Tower' sounds wrong, or it sounds if you are treating 'Tokyo Tower" as a place name or destination - not as a building.

The is often used when multiples of something exist and clarifies that you'll be going to the most obvious one. For example I might say to my nephew "Let's go to the park!" meaning let's go to the park we always go to. If I want to go to the big park downtown I may say "Let's go to Zilker Park!" I would nevver say let's go to The Zilker Park. As for the skytree, probably people haven't often called it "The Tokyo Skytree" but may have called it simply "The Skytree". I mean jeez, how many are there?