For $13.5m, a pinkish-red Greek Revival off Harvard Square. See inside.

Home features five bedrooms, 5.5 baths, six fireplaces, greenhouses, a koi pond, and a heated pool.

It may be in the heart of Cambridge, but 18 Ash St. offers lots of privacy.

Tucked behind brick walls and towering evergreens, the five-bed, 5.5-bath home, which measures 5,376 square feet, is a historic beauty one street off Harvard Square. It’s listed for $13,500,000.

“I think that the most critical thing to this house is that you have a hidden oasis in the middle of Harvard Square. That speaks volumes right there,” said Ed Feijo of Gail Roberts, Ed Feijo & Team at Coldwell Banker Realty, who have the listing. “We just don’t see this level of property with this amount of grounds in this level of finish right there in the square.”

Built in 1854, the luxury home is set on one-third acre with a rolling front lawn under mature trees. A grand foyer welcomes guests with hand-painted murals and a fireplace.

To the left is the 270-square-foot living room, which features another fireplace and tall wood casement windows that overlook the front lawn. A sliding glass door leads to a glass planting room that runs nearly the length of the Harvard Square home. Beyond that, the 140-square-foot library features upscale, lacquered finishes, built-in bookshelves, and a fireplace.

To the right of the foyer is the south-facing dining room, which measures 213 square feet. From there, you can take a half-flight of stairs down into the heated four-season greenhouse, which measures 235 square feet and is filled with lush plants and a koi pond. Next to the greenhouse is the massive 480-square-foot music room, boasting 10-foot ceilings and a fireplace, as well as French doors to the backyard. It also connects to a pantry and mudroom.

The custom kitchen is a dream for any aspiring chef and features a vintage Magic Chef oven that’s been refurbished. The 100-square-foot breakfast area is perfect for busy mornings. A dumbwaiter and catering area are thoughtful amenities.

On the second floor, you’ll find a comfortable home office that measures 222 square feet and features built-in storage. There’s also a family room.

The 190-square-foot primary bedroom suite is the ultimate home resort, complete with a fireplace and two walk-in closets, each measuring 62 square feet. It also features two bathrooms connected by a marble double-steam shower. Nano doors open to the 414-square-foot rooftop terrace, perfect for soaking up the morning sun.

A spiral staircase descends to a side patio, part of the meticulously landscaped grounds, which also provide access to the greenhouse. A patio that sits under a canopy of evergreens is the ideal outdoor spot to enjoy a cup of coffee. It’s next to the heated swimming pool, as well as cabanas and patios, perfect for a New England summer.

“You’re completely in this little hidden oasis back there,” Feijo said.

Back upstairs, the second floor features two additional bedrooms. On the third floor, you’ll find the home’s final two bedrooms and another bath, as well as extensive attic storage and closet space.

The lower level of this Harvard Square home features 789 square feet of storage and utility space, as well as a 129-square-foot exercise room and a 182-square-foot laundry area.