This is where a student must think creatively and use concepts. Think of yourself as being inside a sheep pen. “In the park” means we are within the boundaries (perimeters) of the park, so we are inside those lines. This means we are in a specific space.
If it is a large park, we can make our location less vague by adding more information and “place” prepositions: under the dead oak tree, beside the lake, on the field, in the park. We are always within the park’s boundaries.
Often we say, “I am at the park,” and it can mean the same thing as “I am in the park”, though “at” doesn’t specify if we are inside or outside the boundary. “I am at the park or at the bank, perhaps inside or outside.” This usage is acceptable and must not drive you crazy. Often, we must consider the context or other words of our sentence.
Oh yes! The Brits sometimes say, “I am on the park.” This also means they are in the park!
“On the beach” is a definite location – we are on the surface of the sand and sandy shore of the beach. “I flew a kite on the beach.” “We danced on the beach.”
Sometimes “on the beach” and “at the beach” are interchangeable: “I sunbathed on the beach; I sunbathed at the beach.” At the beach implies the geographical location of the beach in general, not just on the sand, but it is commonly used without English teachers washing our mouths out with soap.
Author: Angel Sgitheanach, Cambly Tutor
If you’d like to keep this conversation going with Angel, give her a call on Cambly or make a reservation with her here: https://www.cambly.com/en/student/tutor/Angel%20Sgitheanach