C# OpenXML how to get Hyperlink from Cell

This will do it for you. Change the foreach loop to whatever you want it to do. Right now it writes the URL to console:

using (SpreadsheetDocument spreadsheet = SpreadsheetDocument.Open(filepath, false))
{
    List<HyperlinkRelationship> hyperlinks = spreadsheet
        .GetAllParts()
        .SelectMany(p => p.HyperlinkRelationships)
        .ToList();

    foreach (HyperlinkRelationship hyperlink in hyperlinks)
    {
        string hyperlink_address = hyperlink.Uri.ToString();
        Console.WriteLine(hyperlink_address);
    }
}

The link you provided actually had the correct solution, it wasn't well formatted in my oppinion though. A little tinkering got me the solution.

This is a "quick and dirty" hack thet will get you the hyperlink behind a cell. For easier comprehension i removed all error handling. A few try/catch blocks and null checks might be advisable in there.... ;)

public static string GetFullHyperlinkValue(SheetData sd, WorksheetPart wsp, string colIdx, int rowIdx)
    {
        // get all hyperlinks - you might want to store them ...
        var hyperlinks = wsp.RootElement.Descendants<Hyperlinks>().First().Cast<Hyperlink>();

        // get the cell at the address
        Cell cell = sd.Descendants<Row>().FirstOrDefault(p => p.RowIndex != null && p.RowIndex == rowIdx).Descendants<Cell>().FirstOrDefault(p => p.CellReference != null && p.CellReference == $"{colIdx}{rowIdx}");

        // get the Hyperlink object "behind" the cell
        Hyperlink hyperlink = hyperlinks.SingleOrDefault(i => i.Reference.Value == cell.CellReference.Value);

        // if the hyperlink has an anchor, the anchor will be stored without the # in hyperlink.Location
        string location = hyperlink.Location;

        // the URI is stored in the HyperlinkRelationship
        HyperlinkRelationship hyperlinkRelationship = wsp.HyperlinkRelationships.SingleOrDefault(i => i.Id == hyperlink.Id);
        var url = hyperlinkRelationship.Uri.ToString();

        return string.IsNullOrWhiteSpace(location) ? url.ToString() : $"{url}#{location}";
    }