Every new student to Hogwarts is astounded, whether they're muggle or halfblood and only heard whispers, or pureblood and were being told stories since they were born. Hogwarts' grounds are huge and beautiful, with a serene lake full of rare and magical species, a chaotic, dangerous forest, neatly trimmed gardens, a Quidditch Pitch and a small train station. It even has a little parking lot, since there's a small magical-and-muggle village nearby that produces a few of students every couple of years. But all of that is nothing compared to the castle itself.
The castle is huge and beautiful and sentient. The stones of the castle are primarily a gray that somehow looks sophisticated and not at all boring, with highlights of windows of turquoise, rose gold, emerald green, gold, and chestnut brown. The castle has quite a few towers, the largest of which are the Ravenclaw and Gryffindor Towers. Although there are tons of rooms, several rather whimsical, each is beautiful with some sort of purpose, and although lots of rooms spend most of their time empty, few carry that lonely, dusty feel, and even then it is overshadowed by the mystery of what interesting things those few dusty rooms might contain. There are tons of classrooms teaching all sorts of different subjects- different magical and non magical languages, math and engineering, philosophy and transfiguration, history and science, potions and chemistry… a huge library and rooms for studying, rooms with wifi and ones with none (very helpful for doing homework), labs and art galleries… the entire place feels a bit like a museum really, stuffed full of art, yet it also feels comfortably lived in.
Unlike other magical schools, since the school itself is sentient, there is no need for some sort of group of statues to decide where for the students to go. After dinner in the Great Hall, the students are sent off to go wander through the castle until they find their new place of residency. Though seeing the staircases move and your friends mysteriously part from you as the school switches it's arrangement of halls and classmates can be scary, it's also incredibly magical.
Because of the technology in the castle, the few roofs of the castle that aren't covered up in roof gardens bursting with hammocked trees and graceful flowers are equipped with colorful stained glass solar panels.
Since there are so many classes, most classes have between ten and twenty people, allowing plenty of energy on the teacher's part to interact with each student individually. Since each student took different classes on different days and a different amount, there was little bonding beyond the houses. The Headmaster implemented two things to remedy this. First, the student exchange program. Once a year, four students in each year, one from each house, would spend a month in a different house. Second, study hour.
During study hour, a student would meet up with three other students from the three other houses in a place of their choice to discuss ideas, work on projects, and give each other advice. Their different house types result in interesting projects and their different personalities balance each other out.
The entire castle was exceeding lovely, full of greenery and windows and interesting people. Mandatory classes on cooking and gardening, which consisted mostly of actually cooking food and tending for plants and not sitting around talking about cooking or caring for plants, kept everyone in good eating and often, mixtures of the four houses would get together for a Quidditch match, a party, a Slytherin vs. Ravenclaw board game, an art showing or concert, or the like. Even the teachers loved the castle. Several of the teachers lived in the castle; those who only had classes part of the day usually lived in the village.
And, of course, it helped that you learnt magic there.