The Horse in Kyoto
The narrator's older brother lives in Kyoto. On vacation, the boy travels there alone and they visit a stable in a nearby forest — where the boy rides a 20-year-old black horse for the first time.
~ことに する means “to decide to do X.” The speaker makes the decision.
~てみる means “try doing something” (give it a go).
Passive 言われる + て means “when I was told (X), …”. A handy N5 set phrase.
~ような + N — “an N as if (something)”. A similative descriptor.
Dictionary form + と means “when / whenever X happens, …”.
An い-adjective in the ~くて form chains to the next adjective or clause.