A task he quite often.....used.... to gather gems for his beloved Rarity, often alongside her but sometimes when she was busy or if he wanted to surprise her he went alone. Today was one of those days.

Word omitted

“What the?” He muttered to himself, moving in closer to explore. It reminded him of the tree of harmony, or even the castle of friendship. But this was far away from both Ponyville and the castle of the two sisters. Curious he began to explore.

Names of a specific person, place, or thing & should be capitalized.