This simple yet effective strategy worked for me. Hope it works for you too!

Go to the world map by clicking Explore->world map,
Then, click on Viridian Meadows->trollsblight caverns,
Now, just keep on clicking retreat and when you get "inspect the area",
You get either a chest or mini health potion!
But what do your pets do while you are doing this? Missions! Do 1 hour ones during the day and longer ones during the night.
You can get thousands of coins just from this strategy!
If you liked this, please donate gold!
(Because I haven't been doing this strategy because I'm preoccupied with the lost grove, I only have about 600k)

Thank you for this advice. I have not been able to make much gold as I have been battling every time they came up. I had not thought to just avoid the battle to find a chest. This has been very helpful to me since I am still a Newbie here.