Fusanosuke

Lower Intermediate Lesson S4 #2 - Giving and Receiving in Japanese-Kureru

お邪魔します--おじゃまします-- (exp) (1) excuse me for disturbing (interrupting) you; (2) greeting used on going to someone's home

This is a polite and formal expression when entering someone's home.  As for the "entering" there are 2 verbs to describe the procedure:

上がる --あがる--to go in, to come in
入る -- はいる -- to enter

The difference is in the threshold. If there is a threshold, then one needs to raise his/her foot to enter the location, hence, 上がる. If there is no threshold, then simple 入る will do.

部屋に入る - enter a room. The floor between a room and a corridor is usually even, one does not need to raise his/her foot.
家に上がる - enter a house. Here most likely there is a threshold or some sort of stairs.
And in each and every textbook there is :
風呂に入る - to take a bath.