The Digital Public Library of America (DPLA) is another powerful aggregated search tool. Like AchiveGrid, it searches across the holdings of many libraries, archives, museums, and other cultural heritage institutions at once. What makes it different from Archive Grid is that this tool searches at the item level (not the collection level), and it focuses on content that is digital and open access, meaning freely available to anyone, anywhere.
While it can be wonderful to have instant access to digitized content, you should think carefully about how much information is lost when an individual item is viewed without the context of the rest of the collection to which it belongs. Without seeing what else is in the collection, and without a finding aid to communicate how an individual item fits in to the bigger picture, you may be missing a lot of information. Whenever possible, pay careful attention to the metadata provided in the DPLA and follow links out to the holding institutions to see if you can find a full finding aid or additional information about the who, what, where, when, why of the collection the item belongs to.
For information on how to search effectively in the DPLA, see their scholarly research guide here: https://dp.la/guides/the-scholarly-research-guide-to-dpla