I like to go to Olympic Park because it’s a good place to exercise. When I go to the park I like to ride my bicycle with my  dad. Olympic Park is large. It has a stamp tour, but I heard it is very hard  because you must walk a lot. I also go to a swimming academy there. The Olympic Park has many visitors every day.  

  Student's sentence            Corrected sentence            Grammar explanation          Better sentence     

Student's Sentence: I like to go to Olympic Park because it’s a good place to exercise.
Corrected Sentence: I like going to Olympic Park because it’s a great place to exercise.
Grammar Explanation: Like going sounds more natural than like to go when talking about a general preference. Great is a more natural adjective in this context.

Better Sentence: I enjoy going to Olympic Park because it’s a perfect place to stay active and exercise.

Student's Sentence: When I go to the park I like to ride my bicycle with my dad.

Corrected Sentence: When I go to the park, I like to ride my bicycle with my dad.

Grammar Explanation: Add a comma after the introductory clause (When I go to the park).

Better Sentence: Whenever I visit the park, I enjoy riding my bicycle with my dad.

Student's Sentence: Olympic Park is large.
Corrected Sentence: Olympic Park is very large.
Grammar Explanation: Adding very makes the description sound more natural and expressive.

Better Sentence Option: Olympic Park is huge and has plenty of space for different outdoor activities.

Student's Sentence: It has a stamp tour, but I heard it is very hard because you must walk a lot.
Corrected Sentence: It has a stamp tour, but I heard it is very challenging because you have to walk a lot.
Grammar Explanation: Very challenging is more appropriate than very hard for describing an activity. Have to is more natural than must in everyday conversation.

Better Sentence Option: It also has a stamp tour, but I heard it’s quite challenging since you need to walk a long distance.

Student's Sentence: I also go to a swimming academy there.
Corrected Sentence: I also attend a swimming academy there.
Grammar Explanation: Attend is the correct verb to use for schools, academies, or classes.

Better Sentence Option: I also attend swimming lessons at a swimming academy in the park.

Student's Sentence: The Olympic Park has many visitors every day.
Corrected Sentence: Olympic Park has many visitors every day.
Grammar Explanation:  The article the is unnecessary before the proper name Olympic Park.

Better Sentence Option: Every day, many people visit Olympic Park to exercise, relax, and enjoy nature.

Better Paragraph
I like going to Olympic Park because it’s a great place to exercise. When I go to the park, I like to ride my bicycle with my dad. Olympic Park is very large. It has a stamp tour, but I heard it is very challenging because you have to walk a lot. I also attend a swimming academy there. Olympic Park has many visitors every day.