For all captive animals, it is ideal to provide a home as similar to the animal's natural environment as possible. This is especially true for tortoises -- including living outdoors. Tortoises are generally best kept in outdoor pens in climates similar to their natural environment (tortoises from arid climates in arid areas; tropical tortoises in tropical areas). If this is not possible, setting up an outdoor pen for at least part of the year is the next best option.
Except for certain circumstances (hatchlings, ill tortoises, tortoises not healthy enough to hibernate), keeping tortoises indoors is the least desirable.
One of the biggest problems with indoor housing is providing adequate floor space. Remember that most tortoises get quite large, so a correspondingly large enclosure is needed. In addition, you'll want something that is relatively easy to clean and that gives you the ability to set up different temperature zones for the tortoise.
Skip the Aquarium
A glass tank is the not the best option for indoor housing. For the majority of turtles, even the largest glass tanks are just too small, and have poor ventilation (and big tanks are hard to maneuver and clean) Tortoises need lots of floor space for roaming around, but the sides just need to be tall enough that the tortoise can't climb over (whereas aquariums tend to have tall sides). Also, unless they are very large, providing a proper temperature gradient for a tortoise is too difficult in a glass tank.
In addition, tortoises seem to prefer non-transparent enclosures - they probably feel very exposed and vulnerable with glass sided tanks, and often spend a lot of time trying to push through the transparent glass as well.
Wood Enclosures - "Turtle Tables"
A homemade wooden enclosure is usually the preferred method for indoor housing.
Essentially, a large wooden box with lots of floor space and fairly short sides is constructed. Typically, UVA/UVB lighting and heat lamps can be suspended over the wooden enclosure to provide the light and heat needs. Some sort of shallow water supply is also necessary. Here are some ideas for building or modifying your own turtle table if you must have your tortoise indoors (size guidelines are listed in some of these):
- Tortoise Trust - a simple but ingenious design that uses plant tray to line the enclosure with varied substrates.
- Pettortoise.co.uk - a very basic small enclosure meant for hatchlings, but this gives a good general idea about constructing a wood home.
For smaller tortoises, some owners use plastic storage containers. These have the advantage of being quite lightweight (so easy to clean) and they come in pretty large sizes these days. However, they do have tall sides so ventilation may become an issue (cutting down the sides or drilling holes for ventilation are options).