[b]Exterior--"[/b]Founded in late 1500s or early 1600s by Mungo Bonham (fw), St. Mungo's Hospital is the primary (and likely only) wizarding hospital in Britain. Located in an abandoned department store in London, the hospital's Healers treat wizards for all sorts of magic-related illnesses and injuries (OP22), and in extreme circumstances has been known to treat Muggles as well (HBP1). The hospital's logo is a wand and a bone, crossed (OP29), and donations are welcome.
The entrance to St. Mungo's is concealed behind an abandoned red-brick London department store called Purge and Dowse, Ltd. on a Muggle street. Unlike, say, the Leaky Cauldron, St. Mungo's is visible to passing Muggles, who merely believe the sign on the front that the store is "Closed for Refurbishment." In the front window, a dummy dressed in outdated styles serves as the gatekeeper; wizards wanting to enter do so by talking to the dummy, and then walking straight through the window (OP22). " taken from the Harry Potter Lexicon
Post Potter Changes--St. Mungos has been extensively updated since the arrival of Khaat and Robert Lupin on staff. A basement and a sub-basement have both been added, rooms added. Furthermore, all the old dingy interior and rickety furniture has been replaced with comfortable contemporary furnishings, bright walls, contemporary lighting, and a pleasant family atmosphere. Departments have been modernized, reorganized and moved from their places in the Potter and Pre-Potter days, though not to the extent of becoming reliant on any sort of "muggle medical nonsense," as some healers have been heard to call it. No modern muggle medical machinery is used, although there are some wizarding variations of some devices.
5th Floor--Hospital Director's Office, Chief of Staff's Office, other administrative offices, Robert Lupin's small potions lab, Small and Large conference rooms, Healer's Lounge, Sunroom/Roof Garden, small owlery, Daycare Center for Employees' children from newborn to age 11.
4th Floor--Isolation Wing for Contagious Diseases
Psychiatric Care Wing
APPARATING IS PERMISSIBLE IN THE HOSPITAL EXCEPT TO OR FROM THIS FLOOR ALONE!
NO ONE ENTERS OR EXITS THIS FLOOR WITHOUT ESCORT BY HOSPITAL PERSONNEL.
THIS ENTIRE FLOOR IS A LOCK DOWN UNIT TO PREVENT ESCAPE.
3rd Floor--OB/GGYN, Delivery Rooms, Surgical Suites, Intensive Care, Pediatrics, Extended Care Unit with Hospice Services available, Sunroom
2nd Floor--Trauma Wing, Noncontagious Diseases, Sunroom
1st Floor--Healer's Clinic--for Walk-In Non Emergent Care, Follow Up Appointments, and other Routine Care. Offices for Other Healers are here as well. Dental Clinic, Mental Health/Counseling Services are located on this floor, separate from the Healers' Clinic.
Ground Floor--Main Entrance, Emergency Care Wing, Gift Shop, Meditation Room, Dining Room with Sunroom, Kitchen, and Dietary Departments, Tea Room, Largest Conference Room--large enough to be used for large fundraising events.
Basement 1--Gym/Spa/Running Track, Pool, Physical Therapy Services, Occupational Therapy Services. Spa has multiple forms of massage, various holistic and magical therapies, and has hot tubs and whirlpools. Tanning Service is provided, but by magical means, not the more harmful muggle methods. Gym has all sorts of exercising equipment and is a full service gym with Personal Trainers available. There are lockers and changing rooms for men and for women here as well, complete with shower facilities.
Basement 2--Morgue/Autopsy/Lab, Large Potions Lab, Storage, heating/cooling equipment.
All floors of St. Mungos have a bank of 4 elevators in the center of the building, in addition to 4 large fireplaces that connect to the Floo network. Elevators and Floos on the 4th floor are blocked from all access except by hospital personnel.
There is a Patient Records Room that is hidden in a secret location in the hospital, guarded by multiple enchantments and is accessible only by the Hospital Director or Chief of Staff.
Messages within the hospital as sent through the use of small paper birds, similar to the paper airplanes used in the Ministry. The paper birds fly up almost right against the ceiling to avoid being in the way of staff and patients. If they are intercepted by someone for whom the message is not intended for, the birds do bite, peck, nip, or self destruct before being read. The only staff members who have the power to intercept any paper bird is the Chief of Staff or the Hospital Director. The birds have been enchanted to merely come and sit on the shoulder of the person for whom the message is intended until the message is retrieved. It is not unusual for staff, particularly those working in Pediatrics, to make notes to themselves, form them into paper birds out of multicolored pieces of paper, and to walk around with the little birds on their shoulders like pets to amuse patients (or themselves if they are bored.)
by 
