Más ciego que un topo
When someone is as blind as a bat, that person is not able to see anything at all, or at least that person has a very poor vision.
There are many expressions that use analogies; as deaf as a doornail, as slow as a turtle, as sly as a fox. Bats are animals which can´t see anything at all. The way they guide themselves while flying is by sonar waves they shout out.
Ni un martillazo más / Es hora de echar la hamaca
This idiom means that it is time to stop work.
People start the day working and spend most of the day working as well. Then, when we call it a day, we mean that it has been enough work for one day and it is time to go home to relax and to save energy for tomorrow´s workday. This idiom could have been coined in the XIX century when people devoted most of their to work.