Open a tmux window in the same working directory

To open a tmux window in the same working directory as your current pane, modify this keybinding in your .tmux.conf:

bind c new-window -c "#{pane_current_path}"

Splits

This can be extended to splits if you want:

bind '"' split-window -c "#{pane_current_path}"
bind % split-window -h -c "#{pane_current_path}"

Source

From this answer at Unix Stack Exchange.