It’s the most wonderful time of the year, at least for architecture and design aficionados. Archtober begins today, and we’re just a few weeks out from the 2019 Open House New York weekend, taking place October 18-20 across all five boroughs. During the three-day event, hundreds of architectural sites and cultural venues will open to the public, including many that are normally off-limits.

Among the new sites that have been added to the docket this year include the High Line Spur, which opened earlier this spring; 277 Mott Street, a retail building designed by Toshiko Mori; Pier 35, a new lower Manhattan park designed by SHoP and Ken Smith Workshop; and 25 Kent, a massive new office complex in Williamsburg.

There will also be some cool special events, including open access to studios and buildings in the Brooklyn Navy Yard, and a day of talks and performances at the TWA Hotel.

You also have a week to prepare for tours that require reservations; they’ll go live on October 8 at 11 a.m. This year, those tours include old favorites—the Woolworth Building and the United Nations Headquarters among them—as well as brand new sites. You can learn about the recent renovations to Central Park’s Belvedere Castle, or visit the New York City outpost of Swedish photography museum Fotografiska, which is located in a landmarked Park Avenue building.

But take note: the process of getting reservations is not easy, and tours regularly fill up within seconds of those going live. (OHNY says that “[w]hat Beyonce is to concerts or Hamilton is to Broadway musicals, OHNY Weekend is to architecture tours,” and they’re not exactly wrong.) The organization has put together a handy guide to getting reservations, but we can tell you from experience that much of it will come down to sheer dumb luck.

The full list of tours that require reservations is here, and you can see every site that will be open over the three-day event on OHNY’s website.