The Pressure Tower is more a curiosity than anything else. It's an inexpensive way to get low mass objects (such as single people) into low orbit briefly, but it is slow and fragile. Pressure Towers are mostly used in amusement parks. There have been proposals to give them to Cargo Cults to allow them easy, maintenance-free access to near orbit.
A pressure tower is a lighter-than-air tube of organic cells each of which acts as a low friction one-way valve for air. This steadily increases the pressure in the tube. As this is a reduction in entropy, the cells use solar power along the length of the tube to generate the energy needed. The top of the tower (some 500 miles up) is capped with a parachute-like structure which redirects the escaping air back down towards the atmosphere, reducing the ecological impact and helping to keep the tower afloat. Waste heat is pumped into the tower (being semi-transparent it is a natural greenhouse as well) which increases the internal pressure.
Each night the tower loses power and slowly deflates, gliding a little downward. In the morning the solar power re-inflates the tower.
To use the tower, enter from the ground and deploy a closed parachute structure over yourself. As air escapes from the top of the tower, the pressure builds up below you, propelling you upwards. As you approach the top of the tower, a sphincter opens the tower's cap, and you are launched into low orbit (along with whatever air leaks out with you). Conveniently, your already deployed parachute can be used to make re-entry substantially more enjoyable.