Glenstone Museum in Potomac, MD. The next block of reservations, for dates in December, will be available Oct. 1. (Iwan Baan/Glenstone Museum)

Reservations for October and November at Glenstone were snapped up within days last week and new spots for December won’t become available until Oct. 1, according to officials at the private art museum and nature preserve.

Glenstone reopens Oct. 4 in Potomac, Md., with expanded galleries, walking paths and visitor amenities including two cafes and an entrance hall. Admission is free but reservations – made on the museum website – are required.

The website began taking reservations on Sept. 4 for dates in October and November. Weekend spots were the first to be taken, but all tickets were gone within 36 hours.

Founded and funded by Mitch and Emily Rales, the private museum focuses on the relationship between art, architecture and landscape. It first opened in 2006 with one gallery and outdoor sculptures on the surrounding hills. The expansion is designed by Thomas Phifer and Partners and features a new building with interlocking galleries surrounding a water court. Among the artists represented are Louise Bourgeois, Cy Twombly and Michael Heizer. Outdoor sculptures from Jeff Koons, Tony Smith and many others dot the 230-acre landscape.

Individuals who were unable to score reservations last week must wait until Oct. 1 to try for December dates. A new statement on the museum’s website notes that “additional tickets are released on the first of every month for the next three months.”

We are fully booked for October and November, so we are not making additional tickets available for those two months, but the website is updated in real time so as people cancel or reduce the number of tickets they reserved, slots become available,” spokeswoman Emily Grebenstein wrote in an email.

Reservations for January will be open Nov. 1.

Glenstone’s hours are Thursdays through Sundays from 10 a.m. to 5 p.m., and reservations can be made for up to 15 people every half hour until 3 p.m. Visitors will be limited to about 400 a day to maintain “an unhurried, uncrowded experience,” according to the museum.