In the USA, and probably Canada, you can land a helicopter anywhere that has not been declared as illegal, with the usual provisos about low flying and reckless operation, but be aware that local restrictions may well override any laid down by the FAA or Transport Canada.
However, making more than four movements at a place in a relatively short time (a movement is a take-off or a landing) makes it a 'feeder site', and subject to strict standards— relevant if you're performing shuttle flights at a special event, such as Epsom races, or the Grand Prix. Pleasure Flying and Feeder Sites are considered elsewhere.
Sites should allow you to make emergency landings without danger to persons or property on the surface, or significant risk to the helicopter and its occupants. An alternate site for a twin should meet single-engined requirements.
Performance Group A (JAR Class 1) helicopters need enough take-off space for the weight to be carried, and take-off, landing and reject areas must be prepared surfaces on which you must be able to land safely before the CDP (see Twins), or continue to an alternative afterwards. You must be able to land safely on the planned area after LDP. Group A (Restricted) (JAR Class 2) machines may have to make a forced landing before CDP or after LDP. For A (Restricted) and B, a prepared surface is not required, but there must be somewhere to land in the event of a reject that will cause no risk to third parties.
The type of takeoff will depend on the size of the area. Class 1 takeoff techniques should be used when the area is restricted, and clear climbout paths should be available (see Twins). They should also be used from elevated sites without obstructions so you can land back on the site if an engine fails before the Critical Decision Point, or make a dive to pick up speed.
The following criteria should apply to all unlicensed sites, which are technical requirements that do not necessarily allow for low flying rules. A congested area is one "substantially used for recreational and residential purposes", etc., which officially makes a golf course one, though you would be forgiven for thinking otherwise. A rule of thumb is 60% buildings and trees, but specifics haven't been tested in court yet, at least not in the UK.
There should be at least one approach and departure lane containing either no or only isolated obstacles—a downwind component is not acceptable. The lanes and landing areas should be big enough to ensure you can land, take off and reach a safe height so you can touch down into wind following an engine failure, while avoiding obstacles by a safe margin.
Try not to have marshland underneath the lanes because, while it may be soft, skids or wheels may sink in during an emergency landing, which is the last place you want dynamic rollover. In other words, the ground beneath the lanes must be suitable for emergency landings with respect to slope, softness, frangible obstructions, etc. Water is OK, provided the performance group is suitable or you've got the usual lifejackets, floats, etc.