Excel's underlying file format structure is also known as BIFF (Binary Interchange File Format). BiffView is a tools for viewing the BIFF structure of a binary Excel sheet.
Download link: http://b2xtranslator.sourceforge.net/snapshots/BiffView.zip
Open the Excel document to analyze:
Then click on the "Create" button. It will generate a similar HTML document:
You can click on the section names to get the details: