Once you have performed Arito's task you can dig for the secret entrance, similar to the way you would look for a tomb. You may pass through the back door to enter the cave, without sacrificing a scimitar. (this is after going back to muhad).
The second "secret" entrance is near the first entrance, on the desert. You'll need a shovel to open the hidden hole. Inside there is a door that can only be opened if you have completed Arito's task. So completing it is necessary to use this entrance. The hole can be found around here
NOTE: To open the hole you might have to dig multiple times on the correct sand tile.
|Muhad||Tribe Leader||✗||Nomad Cave|