Only Up Online, also known as Only Up 3D Parkour: Go Ascend, is a three-dimensional, heart-stopping extreme sports platformer. A player, via an avatar that looks like a girl with reddish-pink hair wearing casual parkour street clothes and gloves, attempts to explore areas of the in-game world that are only reachable by ascending ever higher into the sky on platforms. They perform this feat by completing parkour actions and stunts.�
The player directs their character to walk, run, climb and leap forward. They must use a wide variety of objects hanging in the sky as platforms, including wooden crates and pallets, ocean and highway shipping and transport containers, roof air conditioning units, classic automobiles, doors and frames, metal ladders and pipes, stone paths and walls.
Only Up Online allows the player to save the position of their avatar every now and then at large save-point platforms marked with old computer storage disks. When they do well, they receive achievement medals made of up to three stars for their efforts and reaching certain milestones.
If the avatar falls off a platform, she plummets through the sky until hitting the ocean at the base level. The game then offers the player a restore option to return to the last saved checkpoint.