A blissful situation or period of time is one in which you are extremely happy.
We spent a blissful week together.
我们在一起度过了极为幸福的一周。
If someone is in blissful ignorance of something unpleasant or serious, they are totally unaware of it.
Many country towns were still living in blissful ignorance of the post-war crime wave.
很多乡间小镇对战后的犯罪潮一无所知,依然过着无忧无虑的生活。