An RBXLX file contains a location that defines a place in ROBLOX, an online multiplayer building game. It stores XML information that describes a ROBLOX playing area, which includes 3D models (.RBXM files), tools, parts, teams, and scripts. RBXLX files are similar to .RBXL files but are saved in XML format, which helps reduce the file size.

You can open RBXLX files in ROBLOX Studio by selecting FILE → Open..., choosing the "ROBLOX XML Place Files (*.rbxlx)" file type, and navigating to the location of the RBXLX file. You can create an RBXLX file in ROBLOX Studio by selecting FILE → New. After you make edits to the file, you can save it by selecting FILE → Save or Save As... and choose the "ROBLOX XML Place Files (*.rbxlx)" file type.