/usr/include/mrpt/gui/ is in libmrpt-dev 1:1.4.0-7.
This file is owned by root:root, with mode 0o755.
..
/usr/include/mrpt/gui/include/
/usr/include/mrpt/gui/include/mrpt/
/usr/include/mrpt/gui/include/mrpt/gui/
/usr/include/mrpt/gui/include/mrpt/gui.h
/usr/include/mrpt/gui/include/mrpt/gui/CBaseGUIWindow.h
/usr/include/mrpt/gui/include/mrpt/gui/CDisplayWindow.h
/usr/include/mrpt/gui/include/mrpt/gui/CDisplayWindow3D.h
/usr/include/mrpt/gui/include/mrpt/gui/CDisplayWindowPlots.h
/usr/include/mrpt/gui/include/mrpt/gui/CMyGLCanvasBase.h
/usr/include/mrpt/gui/include/mrpt/gui/WxSubsystem.h
/usr/include/mrpt/gui/include/mrpt/gui/WxUtils.h
/usr/include/mrpt/gui/include/mrpt/gui/gui_frwds.h
/usr/include/mrpt/gui/include/mrpt/gui/keycodes.h
/usr/include/mrpt/gui/include/mrpt/gui/link_pragmas.h
/usr/include/mrpt/gui/include/mrpt/otherlibs/
/usr/include/mrpt/gui/include/mrpt/otherlibs/mathplot/
/usr/include/mrpt/gui/include/mrpt/otherlibs/mathplot/mathplot.h