Caja de las Letras
The Instituto Cervantes, taking advantage of the presence of the vault in the basement of its headquarters in Madrid, uses safe deposit boxes for great figures of Hispanic culture to deposit a legacy that will not be opened until the date they decide. Said compartments would thus perform the functions of a time capsule. The aforementioned building has a vault for having been the former headquarters of the Spanish Central Bank.
| Donor | Date | Opening date | Box no. |
| Francisco Ayala | February 15, 2007 | 2057 | 1032 |
| Antonio Gamoneda | April 20, 2007 | 2032 | 1033 |
| Antoni Tàpies | October 9, 2007 | 2022 | 1031 |
| Carlos Edmundo de Ory | November 6, 2007 | 2022 | 1030 |
| Proyecto Fahrenheit 451 | November 22, 2007 | 2040 | 451 |
| Margarita Salas | February 27, 2008 | 2018 | 1568 |
| Alicia Alonso | April 17, 2008 | 2028 | 1029 |
| Juan Gelman | April 25, 2008 | May 3, 2050 | 1028 |
| Luis García Berlanga | May 27, 2008 | June 2021 | 1034 |
| Pilar de Valderrama | July 13, 2022 | No opening date | 1440 |
| Alejandra Pizarnik | January 22, 2019 | No opening date | 1449 |
| Cristóbal Halffter | January 15, 2009 | 2033 | 1551 |
| Ana María Matute | March 12, 2009 | July 26, 2029 | 1526 |
| Manuel Alexandre | February 18, 2009 | November 11, 2017 | 1534 |
| Juan Marsé | April 21, 2009 | April 21, 2029 | 1533 |
| José Emilio Pacheco | April 21, 2010 | April 21, 2110 | 1525 |
| José Manuel Caballero Bonald | June 7, 2010 | November 11, 2051 | 1543 |
| Carmen Balcells | March 21, 2011 | March 21, 2012 | 1569 |
| Nuria Espert | May 16, 2011 | June 11, 2035 | 1550 |
| Víctor Ullate | June 6, 2011 | June 6, 2161 | 1560 |
| Elena Poniatowska | April 21, 2014 | April 21, 2024 | 1515 |
| Juan Goytisolo | April 21, 2015 | January 5, 2031 | 1500 |
| Fernando del Paso | April 21, 2016 | April 1, 2116 | 1501 |
| Eduardo Mendoza | April 21, 2017 | April 21, 2037 | 1484 |
| John Elliott | October 24, 2017 | June 23, 2037 | 1492 |
| José Balza | September 19, 2019 | September 19, 2059 | 1189 |
| Les Luthiers | October 10, 2019 | September 4, 2042 | 1224 |
| José Hierro | February 22, 2022 | No opening date | 1636 |
| María Victoria Atencia | March 22, 2022 | March 22, 2072 | 1004 |
| Carmen Castellote | April 23, 2022 | No opening date | 1020 |
| Antonio y Manuel Machado | February 9, 2020 | No opening date | 1722 |
| Andrés Bello | December 14, 2020 | December 14, 2020 | 1626 |
| Rafael Cadenas | April 25, 2023 | No opening date | 1287 |
| Leonardo Torres Quevedo | May 5, 2023 | No opening date | 1275 |