Adventure mode is similar to survival, but it has alot of different rules besides from all of the other gamemodes.
Adventure mode is like survival except you cannot break certain blocks without a certain tool. Also not all blocks can be placed on others, so this gamemode is alot harder than survival, and the player can still take damage from falling or other mobs.
Turning on Adventure Mode
A few days after 1.29 came out, Zanzlanz removed the Adventure mode from the main menu, the only way to turn on this gamemode is by commands with "gamemode 2" . Cheats must also be enabled in order to use this gamemode.
The player's inventory in adventure, looks the same just like in Survival