What kinds of scientific investigations involve making observation?

Scientific investigations that involve some kind of testing will make use of observations.  Generally speaking, making observations is the first step of the scientific method.  Based on those observations, a question is asked, and then a hypothesis and prediction will be stated.  A scientist will set up a test, observe the outcome, and collect data on the test.  That will lead the scientist to some kind of conclusion relating to the initial question and hypothesis.  

If the question is asking for a specific type of scientific investigation that relies more on observation and less on experimentation, then a good choice is an investigation about animal behavior.  More specifically, the investigation should focus on observing animals in their natural habitat instead of a lab setting.  This type of scientific investigation will have hypotheses as well, but the scientist is much less able to set up experimental variables and controls.  He or she is dependent on observing the animal behave as it would naturally.  Of course there is a problem with this type of observational investigation too.  The simple presence of the investigator might adversely affect the observations.  If the animals know that the scientist is present in their environment, the animals might behave differently.