Cachly can import GPX files from a number of sources and supports importing of .gpx and .zip files.
The GPX or .zip file will show as attachment. iOS might say "Tap to download". Once downloaded, long press on the file and choose the Share option. Choose the Cachly icon. Cachly will open the import screen where you can select an existing offline list or create a new one.
If a friend has some caches they want to send you, have them do an Export GPX from Cachly and Email the result to you. Then you can do as just described to load them into your Cachly.
Note: Sometimes a GPX file is compressed into a file with a .zip extension. You can treat this just like the above to import. Cachly will take care of unzipping the file.
Once you have downloaded a file from the cloud you can long press the file and choose the Share option. Next choose Cachly and the file will be sent to Cachly and will show the Import screen.
Use the Import from Dropbox option in the More tab to choose a file to import.
You can send a GPX or .zip to Cachly using Airdrop from another device or from macOS. This will bring up a list of apps on your device, choose Cachly and the Import screen will show.
iOS Share Option
If another app has a GPX and provides a Share option you can choose Cachly to send the file.