This is a simple challenge and I am sure a current challenge checker is out there for this one. Find one cache below sea level.

...and same question for this one. Elevation data isn't 100% accurate and not available on Geocaching.com so you need to confirm with your reviewer they are allowing this before we write a checker.

Thanks for your response. I have sent the reviewer a message related to all the elevation caches. I will update once I get the response from the reviewer.

Their are already challenges in US, UK, Australia etc published under the new guidelines.

Here is the checker http://project-gc.com/Challenges/GC6R4TY/23218

It looks to be working. Thanks for your help.