People bring moss indoors expecting a low-effort green and watch it turn brown in a fortnight. It is not that moss is fussy; it is that a normal room is the wrong climate. Here is how to keep it alive inside.
Why it browns on the windowsill
A heated room is dry, and dry air is moss's main enemy indoors. Out in the open it loses water faster than it can take it up, dries out and goes dormant, and if it stays dry it eventually dies rather than just resting. Direct sun through glass finishes it off fast. Open moss in a normal living room is fighting a losing battle.
The reliable answer: a closed terrarium
A lidded glass jar or bowl traps humidity and recycles it, which is exactly what moss wants, and turns it into a near-zero-maintenance feature. This is the honest answer to "moss as a houseplant": grow it behind glass and it thrives for years. See the terrarium guide and the species roundup.
Open dishes and bonsai
If you want moss in the open, on a bonsai or in a shallow dish, you are signing up to mist it daily and keep it out of direct sun and away from radiators. It can be done in a humid room such as a bright bathroom, but it is hands-on. A room sitting at higher humidity, well above half, makes it far easier.
Light
Moss does not want strong light, but it does need some. Bright, indirect light is ideal; deep gloom leaves it weak and prone to algae. A spot near a north window, or a low-output grow light for a closed setup, keeps it healthy without cooking it.