Borobudur attracted attention in 1885, when Yzerman, the Chairman of the Archaeological Society in Yogyakarta, made a discovery about the hidden foot. Photographs that reveal reliefs on the hidden foot were made in 1890–1891.
The discovery led the Dutch East Indies government to take steps to safeguard the monument. In 1900, the government set up a commission consisting of three officials to assess the monument: Brandes, an art historian, Theodoor van Erp, a Dutch army engineer officer, and Van de Kamer, a construction engineer from the Department of Public Works. In 1902, the commission submitted a threefold plan of proposal to the government. First, the immediate dangers should be avoided by resetting the corners, removing stones that endangered the adjacent parts, strengthening the first balustrades and restoring several niches, archways, stupas and the main dome. Second, fencing off the courtyards, providing proper maintenance and improving drainage by restoring floors and spouts. Third, all loose stones should be removed, the monument cleared up to the first balustrades, disfigured stones removed and the main dome restored. The total cost was estimated at that time around 48,800 Dutch guilders.
The restoration then was carried out between 1907 and 1911, using the principles of anastylosis and led by Theodor van Erp. The first seven months of his restoration was occupied with excavating the grounds around the monument to find missing Buddha heads and panel stones. Van Erp dismantled and rebuilt the upper three circular platforms and stupas. Along the way, Van Erp discovered more things he could do to improve the monument; he submitted another proposal that was approved with the additional cost of 34,600 guilders.
At first glance Borobudur had been restored to its old glory. Due to the limited budget, the restoration had been primarily focused on cleaning the sculptures, and Van Erp did not solve the drainage problem. Within fifteen years, the gallery walls were sagging and the reliefs showed signs of new cracks and deterioration. Van Erp used concrete from which alkali salts and calcium hydroxide leached and were transported into the rest of the construction. This caused some problems, so that a further thorough renovation was urgently needed. Small restorations have been performed since then, but not sufficient for complete protection. In the late 1960s, the Indonesian government had requested from the international community a major renovation to protect the monument. In 1973, a master plan to restore Borobudur was created.
The Indonesian government and UNESCO then undertook the complete overhaul of the monument in a big restoration project between 1975–1982. The foundation was stabilized and all 1,460 panels were cleaned. The restoration involved the dismantling of the five square platforms and improved the drainage by embedding water channels into the monument. Both impermeable and filter layers were added. This colossal project involved around 600 people to restore the monument and cost a total of US$ 6,901,243. After the renovation was finished, UNESCO listed Borobudur as a World Heritage Site in 1991