There are many theories regarding the purpose of these lines. Were they built for the gods to see? Or for shamans who “flew” over them in drug induced dreams?
Or did their creators already have means to actually leave the ground, such as balloons?
In any case, from the ground there hardly is anything to see: the area is mostly flat and the figures are of a size that makes it impossible to see them whole from this perspective.
From an airplane, however, they are clearly distinguishable. There are a monkey, a spider, a colibri, even a human figure (often called the “astronaut”).
Of course, over time, erosion must have taken a toll on the lines which are believed to be more than 2000 years old.
By the way, while the lines at Nazca are the most famous ones, there are others in South America, such as the Atacama Giant in Chile, which can be clearly seen from the ground.
According to a CNN report, many new, even bigger and older geoglyphs have been found near Paracas - actually quite close to the Nazca lines.
More:
National Geographic on the Nazca lines: “Ancient, Giant Images Found Carved Into Peru Desert“.
Here is an interesting account by someone who visited the Nazca lines several months before me.
A Spanish blog notes that the lines have now been recorded digitally - a way to preserve them for the foreseeable future and maybe the analysis of the data will yield further insights?!