The easiest exploration feature I can think of is 1-dimensional exploration. Up-down, or left-right, or point A to point B, or room 1 to room 2.

Let's choose the "room" one, like in MUD games.

Requirements

Functional Requirements

• Player can see their character's current room
• Player can move to next rooms by pressing "d" key
• Player can move to previous rooms by pressing "a" key
• There is only 3 rooms and player can only explore that 3 rooms
• Player can see if they can not go to the next/previous room

Technical Requirements

• The toy can be played just by double-clicking an HTML file

Implementation