The malls, Jodd market, Chatucak, Kosan road, river cruise, Chinatown.
As far as walking there are so many issues now. M/B driving the wrong way and on sidewalks, uneven tiles everywhere, metal and wires sticking out from poles that can take your eye out, crosswalks lucky if people stop.
They need to be looking everywhere.
They should be able to get local phone serve from the airport kiosks. The taxis I have taken recently from the airport turn on the meter.