Queen Elizabeth II will celebrate her milestone 90th birthday on April 21. But, it will be work as usual for the British royal who will undertake two engagements in Windsor with her husband Prince Philip, the Duke of Edinburgh. She will unveil a plaque marking The Queen’s Walkway at the foot of Castle Hill.

The 89-year-old British monarch will then meet locals and well-wishers during a walkabout in the town. The walkway is a 6.3 kilometer (nearly 4 miles) walking trail which connects 63 points of significance in Windsor. It was designed by The Outdoor Trust to symbolically recognize the moment Elizabeth became Britain’s longest reigning monarch after more than 63 years on the throne on Sept. 9, 2015.

The same evening, she along with her husband of 68 years, son Prince Charles and his wife Camilla, the Duchess of Cornwall will attend an engagement. A beacon lighting ceremony will be held to celebrate her milestone birthday. Elizabeth will light the principal beacon, and another 1,000 beacons will be lit across the country and worldwide in honor of the queen’s 90th birthday.

Beacons will be taken by the members of the Army Cadet Force to the top of the four highest peaks in the U.K. — Ben Nevis, Scotland; Mount Snowdon, Wales; Scafell Pike, England, and Slieve Donard, Northern Ireland. Meanwhile, in a lead up to her birthday, the queen and her husband will visit the Royal Mail Windsor Delivery Office, to mark the 500th Anniversary of the Postal Service on April 20. The royal couple will meet representatives from Royal Mail and view a demonstration of mail sorting before unveiling a plaque to mark the visit.

Elizabeth and Philip will then visit Alexandra Gardens in Windsor, where they will officially open the new Bandstand and meet children from six local schools. The kids have been involved in designing commemorative plaques for the project. The royal couple will then watch a short performance by a children’s choir.

The queen, who is known to believe in low-key celebrations, will usher in her milestone 90th birthday with her family. However, festivities have been lined up at Windsor castle from May 12-15. It will feature 900 horses and 1,500 performers, including dancers, musicians and choirs, along with well-known artists and actors. Besides, her official birthday will be celebrated with fanfare all over the country in June.