@Ginny Lovegood well I kind of.need help with ideas on the castle and so forth and description!
So, for describing spaces... I recommend you try coming up with adjectives that seem to represent the idea of the place.
Just for the sake of an example, let's say you want to describe Hogwarts. It is a large place, so you have to decide if you want to do a full description or just summarize how the castle looks in general. It might be good to understand how it looks from the point of view of your character (if you are writing with a POV). Either way, you might want to split the castle into different areas such as outskirts, corridors, classrooms, Great Hall, etc. There are several lists of adjectives on the internet; if in doubt, I recommend googling "list of adjectives" or "list of adjectives to describe spaces/places/locations/castles".
Now, if you are writing a brief piece (one paragraph or two) describing the general aspect of the castle, you will need just a few adjectives: one or two for each part of it. Separate the description each part with either a comma or a dot (is that the word?), whatever works better for your text.
On the other hand, if you want to give a longer description (perhaps one paragraph or two for each part of the castle?), you might want to come up with several adjectives. This is trickier because longer descriptions usually (but not always) break the fluidity of the text. If it works for you, though. Perhaps one to four adjectives to describe what your character will pay more attention to, then add your character's feelings towards it. Nobody would pay attention to everything (and no reader will require it from you or your character), so focus on whatever is important to your character or your narrative. Example from my own fic:
As the girl entered the grand entrance doors of the castle, it was all she could think about. She would have loved the castle. Because the younger princess had adored magic from the day she was born. Elsa was only three years old by then, but she would never forget the wonder in her sister's eyes when she looked at the tiny snowflakes the girl had created just for her.
Yes, Anna would have loved studying Hogwarts. She would have appreciated every single one of Elsa's school books; not only the content in each chapter, but its entire craft. The dim light of the candles—because there seemed to be no place for electricity in the school—wouldn't have been intimidating at all, she would have thought of them as an invitation to an adventure. And the moving and talking paintings— if Anna was indeed an art enthusiast, like her tutor and her parents had told her, Elsa was sure she would be beyond words if she set her eyes on them.
Hope it helps. Good luck!