Tāmen zài ɡōnɡyuán lǐ sānbù.
他们在公园里散步。
They went for a stroll in the park.
Notes:
他们(tāmen):they
在(zài): be at
公园(ɡōnɡyuán): park
里(lǐ): inside
散步(sānbù): walk for a stroll
Example:
A:他们去哪儿了?
tāmen qù nǎér le?
wher did they go?
B:他们在公园里散步。
Tāmen zài ɡōnɡyuán lǐ sānbù.
They went for a stroll in the park.