Depending on where you found the link, "SeaMaps" typically refers to one of the following:
Multi-part 7z files work like a puzzle; you cannot open just one piece (like .003) on its own. SeaMaps.7z.003 - BayFiles
The file is a specific segment of a multi-part compressed archive. To access the contents, you must have all pieces of the set (e.g., .001, .002, .003) and use a compatible extraction tool. 📦 How to Extract Multi-Part Files Depending on where you found the link, "SeaMaps"
Place every part in the same directory on your computer. Use 7-Zip: Download and install 7-Zip if you don't have it. Right-click only the first file (the one ending in .001 ). Select 7-Zip > Extract Here or Extract to "SeaMaps" . SeaMaps.7z.003 - BayFiles