美丽的Noun.（people, natural surroundings etc. commonly used） N很美观 (Noun normally refers to decorations ie: 这样摆放很美观)

美丽的 and 美观 are both adjectives, however 美丽 without 的 can be used as noun as well and comes normally after a possessive noun. 美丽的 can describe almost any thing, including people. 美观/美观的 means things that are nice to look at, therefore it is only used to describe things, such as a building, art and so on.

美丽Can describe both people and things,美观main mean a thing, said people would be inaproppriate.