Use reverb. The easiest way to achieve an environmental effect is with reverberation, because it can be done while an instrument is played before post-processing. Reverb is the persistence of sound in a space after the sound is removed. Increasing reverb gives the illusion that the sound is resonating longer. High reverb is akin to recording in a metal room or auditorium, while low reverb simulates recording in a room with cushioned walls to absorb sound. Hook your microphone up to the many amplifiers and effects pedals that allow reverb adjustments.
Use an environmental audio extension. Environmental audio extensions, or EAX, are digital signal processing presets developed by Creative present in Creative sound cards for computers. EAX simulates real world audio environments by adding various effects. EAX programs can be downloaded from the Creative website, if you have a Creative sound card. Use the programs to generate audio spatial effects.
You can also use echo chamber effects pedals. These pedals allow changes in room space, and can add echo, reverb and chorus. The Roland RE-501 and the Maxon DE-01 are audio effects devices that can add spatial effects.
Use echo chambers in post-processing. Garage Band, Pro Tools, Adobe Audition and various other music programs all have methods for creating echo chamber and environment effects. There are many video tutorials available online, depending on which program you are using.