I open the marvel download page https://www.elastic.co/downloads/marvel, but can not find the download URL.
I'm not sure if we ever offered a download link?
You can still get it with bin/plugin -i elasticsearch/marvel/latest as per the docs though.
Thanks. 
We don't provide a link there, but you can find it here - https://www.elastic.co/guide/en/marvel/current/_installation.html#manual_download
I'll see if we can get that fixed though.