深入

She did not merely see the surface, but penetrated beneath.

plunge into the thick of life

go among the masses; immerse oneself among the masses

go down to the grass roots

be deep behind the frontier

make an in-depth analysis

carry out an in-depth investigation; make a thorough investigation

probe into the essence of things

carry on intensive publicity (on sth)

have a deep discussion

intensively launch a movement