It’s about countable versus non-countable nouns: You already know that “the” is not used because “place” is not definite — it’s the first time you’re mentioning it. Therefore, I’ll explain why we need the indefinite article (as opposed to no article). We always need a determiner (usually the indefinite or definite article or a possessive) before a singular countable noun. “Place” is singular and countable, so we say “Tokyo is a good place.” Now that we’ve mentioned “place,” it’s definite: “The place (already identified as Tokyo) is really cool!” “Work” is uncountable (in the usual senses of the word), so no article: “The secret to success is hard work.” “Job” is countable, so we need the article: “The secret to success is a good job.” “He likes beer.” “Beer” is uncountable. We’re talking about beer in general. “He would like (some) beer.” “Beer” is uncountable, the use of “some” is equivalent to the indefinite article, but theoretically could be omitted. In this case, it indicates that we’re not talking about all the beer in the world, but we’re not talking about specific beer either. “He would like a beer.” “Beer” is short for “a glass / bottle / liter / serving of beer,” so it’s countable.

Hi, Yumi! I don't blame you for your confusion. Definite and indefinite articles are one of the hardest parts of English to understand for many English learners. In this sentence, the indefinite article "a" must be included in front of "good place" because Tokyo is not the only good place to see; it is one of many. If you'd like a good resource for indefinite articles, here is a link: http://www.ef.edu/english-resources/english-grammar/indefinite-articles/ I hope my answer helps. Please let me know if you're still confused =)