Check the link below
https://www.vietnamparadisetravel.com/guide/5-days-in-vietnam
I have bookmarked the same for my solo travel later this year.
Almost all hotels in Hanoi offer deals and packages on Halong Bay cruise. You may check with your hotel reception.
Day 1 HANOI ARRIVAL Day 2 HANOI CITY TOUR (B, L) – JOINT IN TOUR
Day 3 HANOI – HOA LU ANCIENT CAPITAL – TRANG AN GROTTOS –
BICH DONG PAGODA (B, L, D) – JOINT IN TOUR
Day 4 HANOI – FREE (B)
Day 5 HANOI – HALONG BAY (B, L, D) – BY SHUTTLE BUS Day 6 HALONG BAY
Day 7 HALONG BAY - HANOI (B, L) – BY SHUTTLE BUS
Day 8 HANOI – FREE(B)
Day 9 HANOI DEPARTURE