This is the 10678th most frequent Russian word.
волшебных
Magical.
In this sentence, "волшебных" is used as an attributive adjective describing the noun "существа" (creatures), giving them the quality of being 'magical'.
Я нашёл книгу о волшебных существах.
I found a book about magical creatures.
Here, "волшебных" is an adjective describing the special and enchanting quality of the 'ten days' experienced.
У нас было волшебных десять дней на берегу моря.
We had a magical ten days by the seaside.
The use of "волшебных" here conveys an adjective describing 'moments' as enchanting and extraordinary.